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Windows: certutil.exe Encodes Files to Base64 Using -encode With Suspicious Extensions

Alert on certutil.exe -encode activity that targets files with suspicious extensions.

FreeReviewedSigma · High · v2
Product
windows
Category
process_creation
Author
Nasreddine Bencherchali (Nextron Systems) (SigmaHQ), DRL 1.1
Published
2023-05-15
Updated
2026-07-31
AnalysisDetection

ATT&CK techniques

Defense Evasion

  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 Windows process executions of certutil.exe where the command line includes the -encode flag and the targeted filename or extension appears in a suspicious list. Base64 encoding can be used to obfuscate file content or stage data for later decoding, reducing visibility for casual inspection. It relies on process creation telemetry, specifically the executable path or original filename plus command-line arguments and embedded file extensions.

Reporting behind it

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Suspicious Archive Extraction From AppData Staging Folder via Process Creation
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Windows: certutil.exe Encodes Files to Base64 Using -encode With Suspicious Extensions
Pivot detection · T1027 · 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.