This joint Cybersecurity Advisory (CSA) is part of an ongoing #StopRansomware effort to publish advisories for network defenders that detail various ransomware variants and ransomware threat actors. These #StopRansomware advisories include recently and historically observed tactics, techniques, and procedures (TTPs) and indicators of compromise (IOCs) to help organizations protect against ransomware. Visit stopransomware.gov to see all #StopRansomware advisories and to learn more about other ransomware threats and no-cost resources.

This guide was developed through the U.S. Joint Ransomware Task Force (JRTF). The JRTF, co-chaired by CISA and FBI, is an interagency, collaborative effort to combat the growing threat of ransomware attacks. The JRTF was launched in response to a series of high-profile ransomware attacks on U.S. critical infrastructure and government agencies. 

The Federal Bureau of Investigation (FBI) and the Cybersecurity and Infrastructure Security Agency (CISA) are releasing this joint Cybersecurity Advisory (CSA) to disseminate known IOCs, TTPs, and detection methods associated with the AvosLocker variant identified through FBI investigations as recently as May 2023. AvosLocker operates under a ransomware-as-a-service (RaaS) model. AvosLocker affiliates have compromised organizations across multiple critical infrastructure sectors in the United States, affecting Windows, Linux, and VMware ESXi environments. AvosLocker affiliates compromise organizations’ networks by using legitimate software and open-source remote system administration tools. AvosLocker affiliates then use exfiltration-based data extortion tactics with threats of leaking and/or publishing stolen data.

The United States National Security Agency (NSA), the U.S. Federal Bureau of Investigation (FBI), the U.S. Cybersecurity and Infrastructure Security Agency (CISA), the Japan National Police Agency (NPA), and the Japan National Center of Incident Readiness and Strategy for Cybersecurity (NISC) (hereafter referred to as the “authoring agencies”) are releasing this joint cybersecurity advisory (CSA) to detail activity of the People’s Republic of China (PRC)-linked cyber actors known as BlackTech. BlackTech has demonstrated capabilities in modifying router firmware without detection and exploiting routers’ domain-trust relationships for pivoting from international subsidiaries to headquarters in Japan and the U.S. — the primary targets. The authoring agencies recommend implementing the mitigations described to detect this activity and protect devices from the backdoors the BlackTech actors are leaving behind.

Social engineering is the attempt to trick someone into revealing information (e.g., a password) or taking an action that can be used to compromise systems or networks. Phishing is a form of social engineering where malicious actors lure victims (typically via email) to visit a malicious site or deceive them into providing login credentials. 

The Cybersecurity and Infrastructure Security Agency (CISA), Federal Bureau of Investigation (FBI), National Security Agency (NSA), and U.S. Department of the Treasury are releasing this fact sheet for senior leadership and operations personnel at operational technology (OT) vendors and critical infrastructure facilities. This fact sheet will assist with better management of risk from OSS use in OT products and increase resilience using available resources. While several resources and recommendations within this fact sheet are best suited for execution by the vendor or the critical infrastructure owner, collaboration across parties will result in less friction for operator workflows and promote a safer, more reliable system and provision of National Critical Functions.