CISA, FBI, NSA, and international agencies have issued an advisory urging organizations and DNS providers to mitigate the Fast Flux evasion technique. Fast Flux, a DNS technique, helps cybercriminals and state-sponsored actors evade detection by rapidly changing DNS records. This technique has been used in various cyberattacks and has been difficult to counter due to its efficiency. By constantly altering DNS records, attackers can make it challenging for defenders to track and block malicious activities such as phishing, malware delivery, and command and control operations.
Fast Flux operates using two types: Single Flux and Double Flux. In Single Flux, attackers frequently rotate the IP addresses associated with a domain name.
Double Flux adds an extra layer of evasion by rotating the DNS name servers in addition to the IP addresses. This method ensures that takedown efforts are even more difficult. The widespread use of Fast Flux is noted across different threat actors, from low-tier cybercriminals to highly sophisticated nation-state actors, making it a pervasive threat in cyberspace.
CISA highlights that Fast Flux is utilized by groups like Gamaredon, Hive ransomware, and Nefilim ransomware. These groups use the technique to evade law enforcement and take down efforts, allowing them to continue their operations. The advisory includes a set of detection measures, urging organizations to analyze DNS logs for frequent IP rotations, low TTL values, and geographically inconsistent resolutions.
Another recommended approach is to integrate external threat feeds and DNS/IP reputation services into firewalls, SIEMs, and DNS resolvers to flag fast flux domains.
For mitigation, CISA recommends using DNS/IP blocklists and firewall rules to block access to Fast Flux infrastructure. Where possible, traffic should be sinkholed to internal servers for further analysis. Other key strategies include using reputational scoring for traffic blocking, centralized logging, and real-time alerting. Participation in information-sharing networks is also crucial for staying ahead of emerging threats. The advisory encourages adopting a multi-layered detection and mitigation strategy to protect critical infrastructure and national security.
