huntrule

Windows: certutil.exe File Encoding to Base64 Using the -encode Flag

Alerts on Windows certutil.exe executions using -encode to base64-encode a file.

FreeReviewedSigma · Medium · v2
Product
windows
Category
process_creation
Author
Florian Roth (Nextron Systems), Jonhnathan Ribeiro, oscd.community, Nasreddine Bencherchali (Nextron Systems) (SigmaHQ), DRL 1.1
Published
2019-02-24
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 process executions of certutil.exe where the command line includes the -encode flag. Encoding file content with built-in Windows tools can be used to transform data for staging or exfiltration, blending into normal administrative activity. It relies on Windows process creation telemetry capturing the executed image name and command-line arguments.

Reporting behind it

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Suspicious Encrypted Implant File Creation for DLL Search Order Hijacking (RainyDay Turian PlugX)
Suspicious PS1Bot PowerShell Payload Written to ProgramData (via file_event)
Malicious Non-Interactive Encoded PowerShell Stager (via process_creation)
Windows: certutil.exe File Encoding to Base64 Using the -encode Flag
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.