# VPNFilter

VPNFilter is malware designed to infect routers and certain network attached storage devices. As of 24 May 2018, it is estimated to have infected approximately 500,000 routers worldwide, though the number of at-risk devices is larger. It can steal data, contains a "kill switch" designed to disable the infected router on command, and is able to persist should the user reboot the router. The FBI believes that it was created by the Russian Fancy Bear group. In February 2022, the CISA announced that a new malware called Cyclops Blink produced by Sandworm had replaced VPNFilter.

## Operation

VPNFilter is malware infecting a number of different kinds of network routers and storage devices. It seems to be designed in part to target serial networking devices using the Modbus protocol to talk to and control industrial hardware, as in factories and warehouses. The malware has special, dedicated code to target control systems using SCADA.
The initial infection vector is still unknown. The Cisco Talos security group hypothesizes the malware exploits known router security vulnerabilities to infect devices.
This software installs itself in multiple stages:
* Stage 1 involves a worm which adds code to the device's crontab (the list of tasks run at regular intervals by the cron scheduler on Linux). This allows it to remain on the device after a reboot, and to re-infect it with the subsequent stages if they are removed. Stage 1 uses known URLs to find and install Stage 2 malware. If those known URLs are disabled, Stage 1 sets up a socket listener on the device and waits to be contacted by command and control systems.
* Stage 2 is the body of the malware, including the basic code that carries out all normal functions and executes any instructions requested by special, optional Stage 3 modules.
* Stage 3 can be any of various "modules" that tell the malware to do specific things, like sniffing network data, gathering credentials, serving as a relay point to hide the origin of subsequent attacks, or collecting data on industrial control devices (Modbus SCADA). Any exfiltrated data can then be encrypted via the Tor network.

## Mitigation

Both Cisco and Symantec suggest that people who own affected devices do a factory reset. That is typically accomplished by using a small, pointed object, such as a straightened out paperclip, to push the small reset button on the back on the unit for 10 to 30 seconds (time varies by model). This will remove the malware, but also restores the router to all original settings. If the router has remote management enabled, a factory reset will often disable this (the default setting of many routers). Remote management is thought to be one possible vector for the initial attack.
Before connecting the factory-reset router to the internet again, the device's default passwords should be changed to prevent reinfection.

## Devices at risk

The initial worm that installs VPNFilter can only attack devices running embedded firmware based on Busybox on Linux compiled only for specific processors. This does not include non-embedded Linux devices such as workstations and servers.
Manufacturer-provided firmware on the following router models is known to be at risk:

### Asus

    RT-AX92U
    RT-AC66U
    RT-N10
    RT-N10E
    RT-N10U
    RT-N56U
    RT-N66U

### D-Link

    DES-1210-08P
    DIR-300
    DIR-300A
    DSR-250N
    DSR-500N
    DSR-1000
    DSR-1000N

### Huawei

    HG8245

### Linksys

    E1200
    E2500
    E3000
    E3200
    E4200
    RV082
    WRVS4400N

### Mikrotik

    CCR1009
    CCR1016
    CCR1036
    CCR1072
    CRS109
    CRS112
    CRS125
    RB411
    RB450
    RB750
    RB911
    RB921
    RB941
    RB951
    RB952
    RB960
    RB962
    RB1100
    RB1200
    RB2011
    RB3011
    RB Groove
    RB Omnitik
    STX5
    Mikrotik RouterOS versions up to 6.38.5 on current or 6.37.5 on bugfix release chains

### Netgear

    DG834
    DGN1000
    DGN2200
    DGN3500
    FVS318N
    MBRN3000
    R6400
    R7000
    R8000
    WNR1000
    WNR2000
    WNR2200
    WNR4000
    WNDR3700
    WNDR4000
    WNDR4300
    WNDR4300-TN
    UTM50

### QNAP

    TS251
    TS439 Pro
    Other QNAP NAS devices running QTS software

### TP-Link

    R600VPN
    TL-WR741ND
    TL-WR841N

### Ubiquiti

    NSM2
    PBE M5

### Upvel

    Unknown Models

### ZTE

    ZXHN H108N

### Epidemiology

VPNFilter is described by Cisco Talos as having infected as many as 500,000 devices worldwide, in perhaps 54 different countries, though proportionately the focus has been on Ukraine.

## FBI investigation

The FBI has taken a high-profile role in addressing this malware, conducting an investigation that resulted in the seizure of the domain name toknowall.com as ostensibly having been used to redirect queries from stage 1 of the malware, allowing it to locate and install copies of stages 2 and 3. The US Justice Department also compelled the site Photobucket to disable known URLs used to distribute malware Stage 2.

### FBI recommendation on removing the infection

On 25 May 2018, the FBI recommended that users reboot their at-risk devices. This would temporarily remove the stages 2 and 3 of the malware. Stage 1 would remain, leading the router to try re-downloading the payload and infecting the router again. However, prior to the recommendation the US Justice Department seized web endpoints the malware uses for Stage 2 installation.
Without these URLs, the malware must rely on the fallback socket listener for Stage 2 installation. This method requires threat actor command and control systems to contact each system to install Stage 2, increasing the threat actor's risk of being identified. The FBI further recommended users disable remote management on their devices and update the firmware. A firmware update removes all stages of the malware, though it is possible the device could be reinfected.
The FBI said that this would help them to find the servers distributing the payload.