Process Doppelgänging

Adversaries may inject malicious code into process via process doppelgänging in order to evade process-based defenses as well as possibly elevate privileges. Process doppelgänging is a method of executing arbitrary code in the address space of a separate live process. 

Windows Transactional NTFS (TxF) was introduced in Vista as a method to perform safe file operations. (Citation: Microsoft TxF) To ensure data integrity, TxF enables only one transacted handle to write to a file at a given time. Until the write handle transaction is terminated, all other handles are isolated from the writer and may only read the committed version of the file that existed at the time the handle was opened. (Citation: Microsoft Basic TxF Concepts) To avoid corruption, TxF performs an automatic rollback if the system or application fails during a write transaction. (Citation: Microsoft Where to use TxF)

Although deprecated, the TxF application programming interface (API) is still enabled as of Windows 10. (Citation: BlackHat Process Doppelgänging Dec 2017)

Adversaries may abuse TxF to a perform a file-less variation of [Process Injection](https://attack.mitre.org/techniques/T1055). Similar to [Process Hollowing](https://attack.mitre.org/techniques/T1055/012), process doppelgänging involves replacing the memory of a legitimate process, enabling the veiled execution of malicious code that may evade defenses and detection. Process doppelgänging's use of TxF also avoids the use of highly-monitored API functions such as <code>NtUnmapViewOfSection</code>, <code>VirtualProtectEx</code>, and <code>SetThreadContext</code>. (Citation: BlackHat Process Doppelgänging Dec 2017)

Process Doppelgänging is implemented in 4 steps (Citation: BlackHat Process Doppelgänging Dec 2017):

* Transact – Create a TxF transaction using a legitimate executable then overwrite the file with malicious code. These changes will be isolated and only visible within the context of the transaction.
* Load – Create a shared section of memory and load the malicious executable.
* Rollback – Undo changes to original executable, effectively removing malicious code from the file system.
* Animate – Create a process from the tainted section of memory and initiate execution.

This behavior will likely not result in elevated privileges since the injected process was spawned from (and thus inherits the security context) of the injecting process. However, execution via process doppelgänging may evade detection from security products since the execution is masked under a legitimate process. 

Platforms: Windows
Tactics:
phase_name: defense-evasion
phase_name: privilege-escalation

Detection:
Monitor and analyze calls to <code>CreateTransaction</code>, <code>CreateFileTransacted</code>, <code>RollbackTransaction</code>, and other rarely used functions indicative of TxF activity. Process Doppelgänging also invokes an outdated and undocumented implementation of the Windows process loader via calls to <code>NtCreateProcessEx</code> and <code>NtCreateThreadEx</code> as well as API calls used to modify memory within another process, such as <code>WriteProcessMemory</code>. (Citation: BlackHat Process Doppelgänging Dec 2017) (Citation: hasherezade Process Doppelgänging Dec 2017)

Scan file objects reported during the PsSetCreateProcessNotifyRoutine, (Citation: Microsoft PsSetCreateProcessNotifyRoutine routine) which triggers a callback whenever a process is created or deleted, specifically looking for file objects with enabled write access. (Citation: BlackHat Process Doppelgänging Dec 2017) Also consider comparing file objects loaded in memory to the corresponding file on disk. (Citation: hasherezade Process Doppelgänging Dec 2017)

Analyze process behavior to determine if a process is performing actions it usually does not, such as opening network connections, reading files, or other suspicious actions that could relate to post-compromise behavior.

References:
source_name: mitre-attack
description: Microsoft. (n.d.). Transactional NTFS (TxF). Retrieved December 20, 2017.
source_name: Microsoft TxF
description: Microsoft. (n.d.). Basic TxF Concepts. Retrieved December 20, 2017.
source_name: Microsoft Basic TxF Concepts
description: Microsoft. (n.d.). When to Use Transactional NTFS. Retrieved December 20, 2017.
source_name: Microsoft Where to use TxF
description: Liberman, T. & Kogan, E. (2017, December 7). Lost in Transaction: Process Doppelgänging. Retrieved December 20, 2017.
source_name: BlackHat Process Doppelgänging Dec 2017
description: hasherezade. (2017, December 18). Process Doppelgänging – a new way to impersonate a process. Retrieved December 20, 2017.
source_name: hasherezade Process Doppelgänging Dec 2017
description: Microsoft. (n.d.). PsSetCreateProcessNotifyRoutine routine. Retrieved December 20, 2017.
source_name: Microsoft PsSetCreateProcessNotifyRoutine routine