RSS feed source: US Computer Emergency Readiness Team

Executive summary

Many networks have a gap in their defenses for detecting and blocking a malicious technique known as “fast flux.” This technique poses a significant threat to national security, enabling malicious cyber actors to consistently evade detection. Malicious cyber actors, including cybercriminals and nation-state actors, use fast flux to obfuscate the locations of malicious servers by rapidly changing Domain Name System (DNS) records. Additionally, they can create resilient, highly available command and control (C2) infrastructure, concealing their subsequent malicious operations. This resilient and fast changing infrastructure makes tracking and blocking malicious activities that use fast flux more difficult. 

The National Security Agency (NSA), Cybersecurity and Infrastructure Security Agency (CISA), Federal Bureau of Investigation (FBI), Australian Signals Directorate’s Australian Cyber Security Centre (ASD’s ACSC), Canadian Centre for Cyber Security (CCCS), and New Zealand National Cyber Security Centre (NCSC-NZ) are releasing this joint cybersecurity advisory (CSA) to warn organizations, Internet service providers (ISPs), and cybersecurity service providers of the ongoing threat of fast flux enabled malicious activities as a defensive gap in many networks. This advisory is meant to encourage service providers, especially Protective DNS (PDNS) providers, to help mitigate this threat by taking proactive steps to develop accurate, reliable, and timely fast flux detection analytics and blocking capabilities for their customers. This CSA also provides guidance on detecting and mitigating elements of

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RSS feed source: US Computer Emergency Readiness Team

Summary

Note: This joint Cybersecurity Advisory is part of an ongoing #StopRansomware effort to publish advisories for network defenders detailing 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.

The Federal Bureau of Investigation (FBI), Cybersecurity and Infrastructure Security Agency (CISA), and the Multi-State Information Sharing and Analysis Center (MS-ISAC) are releasing this joint advisory to disseminate known Medusa ransomware TTPs and IOCs, identified through FBI investigations as recently as February 2025. 

Medusa is a ransomware-as-a-service (RaaS) variant first identified in June 2021. As of February 2025, Medusa developers and affiliates have impacted over 300 victims from a variety of critical infrastructure sectors with affected industries including medical, education, legal, insurance, technology, and manufacturing. The Medusa ransomware variant is unrelated to the MedusaLocker variant and the Medusa mobile malware variant per the FBI’s investigation.

FBI, CISA, and MS-ISAC encourage organizations to implement the recommendations in the Mitigations section of this advisory to reduce the likelihood and impact of Medusa ransomware incidents.

Download the PDF version of this report:

For a downloadable list of IOCs, see:

AA25-071A STIX XML (XML, 34.30 KB )

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