huntrule

Webserver log detection of Log4j CVE-2021-44228 JNDI payloads in User-Agent, URI query, or Referer

Flags webserver requests with ${jndi:...} payloads in User-Agent, URI query, or Referer indicative of Log4Shell attempts.

FreeReviewedSigma · High · v5
Category
webserver
Author
Florian Roth (Nextron Systems) (SigmaHQ), DRL 1.1
Published
2021-12-10
Updated
2026-07-31
AnalysisDetection

ATT&CK techniques

Initial Access

  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 web requests whose User-Agent, URI query string, or Referer fields contain patterns consistent with Log4Shell-style JNDI lookup payloads associated with CVE-2021-44228. Such strings can indicate an attacker attempting to trigger remote lookup behavior via vulnerable log processing. It relies on webserver log telemetry and searches for known obfuscation and JNDI indicator substrings in those specific HTTP fields.

Reporting behind it

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Possible Citrix Bleed Session Token Leak via OpenID Configuration Endpoint (CVE-2023-4966) (via webserver)
Webserver log detection of Log4j CVE-2021-44228 JNDI payloads in User-Agent, URI query, or Referer
Pivot detection · T1190 · 9 related

Changelog

v5
  1. v5
    Candidate ingested via manual entry.2026-07-31
  2. v4
    Candidate ingested via manual entry.2026-07-31
  3. v3
    Candidate ingested via manual entry.2026-07-31
  4. v2
    Candidate ingested via manual entry.2026-07-31
  5. 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.