Ever Heard of Fast Flux? Here’s Why It Matters in Cybersecurity
- Hamed Mirjahanshahi
- Apr 9
- 1 min read
Fast flux is a technique used by cybercriminals to hide phishing sites, malware distribution, or command-and-control (C2) servers by rapidly changing the IP addresses associated with a single domain name. It’s like playing hide-and-seek with security teams!
Here’s how it works:
A domain name (like malicious-site[.]com) is registered.
That domain is linked to many different IP addresses.
The DNS records for that domain are set with a very short TTL (time to live), as short as a few minutes or seconds.
As a result, each DNS query returns a different IP address, constantly rotating through a large pool.
There are two main types:
Single-flux: Only the A records (IP addresses) change frequently.
Double-flux: Both the A records and NS records (name servers) change, making it even harder to track or block.
Why it’s dangerous:
Makes it hard for security tools to block malicious domains, since the IPs are always changing.
It’s often used with botnets for resilient malware hosting or C2 communication.
How to spot & stop it:
Monitor DNS traffic for frequent IP changes & inconsistent geolocation
Use threat intel feeds & Protective DNS (PDNS) services
Implement DNS filtering & anomaly detection
Watch for domains with TTLs set between 3–5 minutes
Analyze DNS traffic to understand normal vs. suspicious behavior
And don’t forget to monitor DNS over TLS (DoT), as cybercriminals often use it to conceal their footprint.