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The Sandworm actor has replaced the exposed VPNFilter malware with a new more advanced framework.


The UK National Cyber Security Centre (NCSC), the Cybersecurity and Infrastructure Security Agency (CISA), the National Security Agency (NSA) and the Federal Bureau of Investigation (FBI) in the US have identified that the actor known as Sandworm or Voodoo Bear is using a new malware, referred to here as Cyclops Blink. The NCSC, CISA, FBI and NSA have previously attributed the Sandworm actor to the Russian GRU’s Main Centre for Special Technologies GTsST.

The malicious cyber activity below has previously been attributed to Sandworm:

Cyclops Blink appears to be a replacement framework for the VPNFilter malware exposed in 2018, which exploited network devices, primarily small office/home office (SOHO) routers, and network attached storage (NAS) devices.

This advisory summarises the VPNFilter malware it replaces, and provides more detail on Cyclops Blink, as well as the associated tactics, techniques and procedures (TTPs) used by Sandworm. An NCSC malware analysis report on Cyclops Blink is also available and can be read in parallel.

It also points to mitigation measures to help organisations that may be affected by this malware.


First exposed in 2018

A series of articles published by Cisco Talos in 2018 describes VPNFilter and its modules in detail. VPNFilter was deployed in stages, with most functionality in the third-stage modules. These modules enabled traffic manipulation, destruction of the infected host device, and likely enabled downstream devices to be exploited. They also allowed monitoring of Modbus SCADA protocols, which appears to be an ongoing requirement for Sandworm, as also seen in their previous attacks against ICS networks.

VPNFilter targeting was widespread and appeared indiscriminate, with some exceptions: Cisco Talos reported an increase of victims in Ukraine in May 2018. Sandworm also deployed VPNFilter against targets in the Republic of Korea before the 2018 Winter Olympics.

In May 2018 Cisco Talos published the blog that exposed VPNFilter, and the US Department of Justice linked the activity to Sandworm, and announced its disruption of the botnet.

Activity since its exposure

A Trendmicro blog in January 2021 detailed residual VPNFilter infections and provided data showing a reduction in requests to a known C2 domain. Since the disruption in May 2018, Sandworm has shown limited interest in existing VPNFilter footholds, instead preferring to retool.

Cyclops Blink

Active since 2019

The NCSC, CISA, FBI and NSA, along with industry partners, have now identified a large-scale modular malware framework which is affecting network devices. The new malware is referred to here as Cyclops Blink and has been deployed since at least June 2019, fourteen months after VPNFilter was disrupted. In common with VPNFilter, Cyclops Blink deployment also appears indiscriminate and widespread.

The actor has so far primarily deployed Cyclops Blink to WatchGuard devices, but it is likely that Sandworm would be capable of compiling the malware for other architectures and firmware.


Note that only WatchGuard devices that were reconfigured from the manufacturer default settings to open remote management interfaces to external access could be infected

Malware overview

The malware itself is sophisticated and modular with basic core functionality to beacon (T1132.002) device information back to a server and enable files to be downloaded and executed. There is also functionality to add new modules while the malware is running, which allows Sandworm to implement additional capability as required.

The NCSC has published a malware analysis report on Cyclops Blink which provides more detail about the malware.

Post exploitation

Post exploitation, Cyclops Blink is generally deployed as part of a firmware ‘update’ (T1542.001). This achieves persistence when the device is rebooted and makes remediation harder.

Victim devices are organised into clusters and each deployment of Cyclops Blink has a list of command and control (C2) IP addresses and ports that it uses (T1008). All the known C2 IP addresses to date have been used by compromised WatchGuard firewall devices. Communications between Cyclops Blink clients and servers are protected under Transport Layer Security (TLS) (T1071.001), using individually generated keys and certificates. Sandworm manages Cyclops Blink by connecting to the C2 layer through the Tor network:


Cyclops Blink persists on reboot and throughout the legitimate firmware update process. Affected organisations should therefore take steps to remove the malware.

WatchGuard has worked closely with the FBI, CISA and the NCSC, and has provided tooling and guidance to enable detection and removal of Cyclops Blink on WatchGuard devices through a non-standard upgrade process.  Device owners should follow each step in these instructions to ensure that devices are patched to the latest version and that any infection is removed.

The WatchGuard tooling and guidance is available at:

In addition:

  • If your device is identified as infected with Cyclops Blink, you should assume that any passwords present on the device have been compromised and replace them (see NCSC password guidance for organisations).
  • You should ensure that the management interface of network devices is not exposed to the internet.

In addition:

  • If your device is identified as infected with Cyclops Blink, you should assume that any passwords present on the device have been compromised and replace them (see the NCSC’s password guidance for organisations)
  • You should ensure that the management interface of network devices is not exposed to the internet

Indicators of compromise

Please refer to the accompanying Cyclops Blink malware analysis report for indicators of compromise which may help to detect this activity.


This advisory has been compiled with respect to the MITRE ATT&CK® framework, a globally accessible knowledge base of adversary tactics and techniques based on real-world observations.

Tactic Technique Procedure
Initial Access T1133 External Remote Services

  • The actors most likely deploy modified device firmware images by exploiting an externally available service
Execution T1059.004 Command and Scripting Interpreter: Unix Shell

  • Cyclops Blink executes downloaded files using the Linux API
Persistence T1542.001 Pre-OS Boot: System Firmware

  • Cyclops Blink is deployed within a modified device firmware image
T1037.004 Boot or Logon Initialisation Scripts: RC Scripts

  •  Cyclops Blink is executed on device startup, using a modified RC script
Defence Evasion T1562.004 Impair Defenses: Disable or Modify System Firewall

  • Cyclops Blink modifies the Linux system firewall to enable C2 communication
T1036.005 Masquerading: Match Legitimate Name or Location

  • Cyclops Blink masquerades as a Linux kernel thread process
Discovery T1082 System Information Discovery

  • Cyclops Blink regularly queries device information
Command and Control T1090 Proxy
T1132.002 Data Encoding: Non-Standard Encoding

  • Cyclops Blink command messages use a custom binary scheme to encode data
T1008 Fallback Channels

  • Cyclops Blink randomly selects a C2 server from contained lists of IPv4 addresses and port numbers
T1071.001 Application Layer Protocol: Web Protocols

  • Cyclops Blink can download files via HTTP or HTTPS
T1573.002 Encrypted Channel: Asymmetric Cryptography

  • Cyclops Blink C2 messages are individually encrypted using AES-256-CBC and sent underneath TLS
T1571 Non-Standard Port

  • The list of port numbers used by Cyclops Blink includes non-standard ports not typically associated with HTTP or HTTPS traffic
Exfiltration T1041 Exfiltration Over C2 Channel

  • Cyclops Blink can upload files to a C2 server


A Cyclops Blink infection does not mean that an organisation is the primary target, but it may be selected to be, or its machines could be used to conduct attacks.

Organisations are advised to follow the mitigation advice in this advisory and to refer to indicators of compromise (not exhaustive) in the Cyclops Blink malware analysis report to detect possible activity on networks.

UK organisations affected by the activity outlined in this advisory should report any compromises to the NCSC via their website.

Source: National Cyber Security Centre

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