Suspicious WarmCookie C2 Beacon With Fixed Firefox User-Agent

ATT&CK techniques

C2

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
C2
- T1071.001Web Protocols
Exfiltration
Impact

What it detects

This rule detects web traffic carrying the hardcoded Firefox 115.0 User-Agent string used by WarmCookie. WarmCookie beaconed to its command-and-control servers with a fixed Mozilla Firefox 115.0 User-Agent regardless of the host browser. A single static outdated User-Agent applied to all C2 requests is an application-layer protocol indicator that stands out from real browser diversity.

Reporting behind it

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Suspicious WarmCookie C2 Beacon With Fixed Firefox User-Agent

Pivot detection · T1071.001 · 9 related

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

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