Today, CISA—in partnership with the National Security Agency (NSA), 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’s National Cyber Security Centre (NCSC-NZ)—released joint Cybersecurity Advisory Fast Flux: A National Security Threat (PDF, 841 KB). This advisory warns organizations, internet service providers (ISPs), and cybersecurity service providers of the ongoing threat of fast flux enabled malicious activities and provides guidance on detection and mitigations to safeguard critical infrastructure and national security.

“Fast flux” is a technique used to obfuscate the locations of malicious servers through rapidly changing Domain Name System (DNS) records associated with a single domain name. This threat exploits a gap commonly found in network defenses, making the tracking and blocking of malicious fast flux activities difficult.

The authoring agencies strongly recommend adopting a multi-layered approach to detection and mitigation to reduce risk of compromise by fast flux-enabled threats. Service providers, especially Protective DNS providers (PDNS), should track, share information about, and block fast flux as part of their provided cybersecurity services. Government and critical infrastructure organizations should close this ongoing gap in network defenses by using cybersecurity and PDNS services that block malicious fast flux activity.

For more information on PDNS services, see Selecting a Protective DNS Service.

https://www.cisa.gov/news-events/alerts/2025/04/03/nsa-cisa-fbi-and-international-partners-release-cybersecurity-advisory-fast-flux-national-security