huntrule

Suspicious Malware User-Agent Strings in Proxy Logs

Alerts on proxy traffic with user-agent values and substrings commonly seen in malware communications.

FreeReviewedSigma · High · v2
Category
proxy
Author
Florian Roth (Nextron Systems), X__Junior (Nextron Systems), Nasreddine Bencherchali (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 HTTP requests whose user agent matches a hard-coded set of known suspicious or malware-associated strings and patterns. Attackers may use atypical or impersonated user agents to blend in with normal web traffic while reaching command-and-control or delivering payloads. The detection relies on proxy telemetry that includes the client user agent field, matching it against the specified values and wildcards.

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)
Suspicious Malware User-Agent Strings in Proxy Logs
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.