huntrule

Proxy logs: suspicious exploit framework User-Agent strings

High-severity match on proxy User-Agent strings commonly seen in exploit/pentest frameworks.

FreeReviewedSigma · High · v2
Category
proxy
Author
Florian Roth (Nextron Systems) (SigmaHQ), DRL 1.1
Published
2017-07-08
Updated
2026-07-31
AnalysisDetection

ATT&CK techniques

C2

  1. Recon

  2. Resource Dev

  3. Initial Access

  4. Execution

  5. Persistence

  6. Priv Esc

  7. Defense Evasion

  8. Cred Access

  9. Discovery

  10. Lateral Movement

  11. Collection

  12. C2

  13. Exfiltration

  14. Impact

What it detects

This rule flags proxy traffic where the User-Agent header matches specific patterns commonly used by exploit and pentest frameworks (for example, Metasploit- and Cobalt Strike-associated strings), as well as generic exploit-related markers. Such traffic matters because unusual or highly patterned User-Agent values can indicate automated tooling used for command-and-control, reconnaissance, or exploitation. It relies on proxy log telemetry containing a client User-Agent field and compares it against a defined set of suspicious string matches.

Reporting behind it

Related detections9 linkedT1071.001 — drag to rearrange
Malicious Cobalt Strike Default Named Pipe Activity
Malicious VoidLink Kernel Rootkit C2 Endpoints via HTTP (via proxy)
Malicious EtherRAT C2 Exfiltration Endpoints via HTTP (via proxy)
Possible PlugX and NPS Proxy Command and Control Domain Lookup
Possible Backdoor Mistic Command and Control Domain Lookup
Suspicious Weaver Ant In-Memory Web Shell Marker in Web Request (via webserver)
Malicious BlueNoroff C2 Communication via cur1-agent User-Agent (via proxy)
Possible GammaSteel C2 Using Spoofed iPhone User Agent
Suspicious PolarEdge Backdoor C2 URL with Module and putdata Command (via proxy)
Proxy logs: suspicious exploit framework User-Agent strings
Pivot detection · T1071.001 · 9 related

Changelog

v2
  1. v2
    Candidate ingested via manual entry.2026-07-31
  2. v1
    No changelog recorded for this version.2026-07-30

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