Malicious servers being disguised through the quick-changing technique known as "fast flux" is alerted by CISA and FBI.
In the ever-evolving world of cybersecurity, the fast flux DNS technique continues to pose a significant challenge for security operations teams. This technique, which involves rapidly rotating DNS records with very short TTLs to make malicious networks harder to take down or trace, remains actively used by sophisticated cyber threat actors to maintain resilient and evasive command-and-control (C2) infrastructure [2].
The fast flux method, which can take two forms - single flux, where a single domain name is associated with multiple IP addresses, and double flux, where both the domain name and DNS name server are changed - has been employed by a variety of threat actors. Among them, Trident Ursa, a group known for its activities during the early days of the Russian invasion of Ukraine, has been observed using fast flux to mask threat activities [1].
While the search results do not explicitly mention Trident Ursa's current use of fast flux, the broader trend in 2025 indicates that advanced threat groups, including ransomware and malware operators, continue to leverage fast flux for infrastructure resilience, often combined with AI to automate switching and evasion [1][3].
Other notable threat groups historically associated with advanced infrastructure tactics, such as Hive and Nefilim, are likely still using or adapting fast flux techniques to sustain their operations and avoid disruption [5]. The rising trend of fast flux use among ransomware actors noted in Q2 2025 ransomware analysis suggests that these groups continue to employ this technique.
The FBI, CISA, and international partners have issued a warning about cyber threat groups using a technique called "fast flux." To combat this, several defensive strategies have been proposed. Implementing anomaly detection systems for DNS query logs, increasing logging and monitoring of DNS traffic, using threat intelligence feeds to identify known fast flux domains and related IP addresses, and sinkholing malicious domains are all suggested steps for detection and mitigation [4].
Defensive strategies now rely heavily on AI and network visibility tools to detect patterns typical of fast flux usage, such as irregular DNS behaviours, TLS handshake anomalies, and dynamic IP reputation shifts [3]. The use of AI-enhanced fast flux attacks is increasing, with attackers automating C2 rotation and exfiltration vectors to evade detection and mitigate defense efforts [1][3].
In summary, fast flux DNS remains a critical and evolving tool for threat actors like Trident Ursa, Hive, and Nefilim, facilitating infrastructure resilience in 2025. This technique is increasingly fused with AI to automate and enhance evasion, representing a significant cybersecurity challenge requiring advanced, AI-driven defense mechanisms.
- The fast flux technique, employed by threat actors such as Trident Ursa, Hive, and Nefilim, continues to challenge cybersecurity in 2025, with advanced groups like ransomware and malware operators leveraging it for infrastructure resilience.
- To combat fast flux DNS attacks, security operations teams rely on defensive strategies that include implementing anomaly detection systems, increasing logging and monitoring of DNS traffic, using threat intelligence feeds, and sinkholing malicious domains.
- In the general-news and crime-and-justice sectors, the FBI, CISA, and international partners have issued warnings about cyber threat groups using fast flux, a method that is now often combined with AI to automate switching and evasion.
- Ransomware actors, as noted in Q2 2025 ransomware analysis, are increasingly using the fast flux technique, making it a significant threat that warrants the development of AI-driven defense mechanisms for technology-reliant security operations.
