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 axios NPM Supply Chain C2 Domain Resolution
Suspicious Reverse Shell via Dev TCP or Netcat
Malicious HarborWatch RAT Command and Control Beacon by User Agent (via proxy)
Suspicious UAT-10608 Credential Harvesting C2 Beacon via HTTP
Malicious BadIIS C2 Communication via lwxatisme User-Agent
Possible PS1Bot C2 Beacon With Drive Serial URI Pattern (via proxy)
Suspicious WarmCookie C2 Beacon With Fixed Firefox User-Agent
Malicious Renamed Python Interpreter Executing nvidia.py RAT
Malicious Self-Signed TLS Certificate With Exploit Subject via Zeek X509
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.