huntrule

Windows Rundll32 Execution Masquerading as Image Files via Image Extensions

Flags rundll32.exe executions whose command line references image file extensions used for DLL masquerading.

FreeReviewedSigma · High · v1
Product
windows
Category
process_creation
Author
Hieu Tran (SigmaHQ), DRL 1.1
Published
2023-03-13
Updated
2026-07-30
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 identifies process creation events where rundll32.exe is executed while the command line includes common image file extensions (e.g., .png, .jpg, .gif). Attackers may use rundll32 to load DLL functionality while disguising the argument as an image to evade casual inspection and some content-based defenses. The detection relies on Windows process creation telemetry, matching the image path/end with rundll32.exe (and OriginalFileName) and the presence of specified image extensions in the command line.

Reporting behind it

Related detections9 linkedT1218.011 — drag to rearrange
Malicious Zardoor Backdoor Execution via rundll32 (via process_creation)
Malicious Rundll32 Loading an Export From a User Path (via process_creation)
Renamed Regsvr32 or Rundll32 Loading a DLL With a Non-Standard Extension (via process_creation)
Malicious Rundll32 DllRegisterServer Execution From a User-Writable Path (via process_creation)
IMEEX Framework DLL Execution via Rundll32 Loading imaadp (via process_creation)
Suspicious Persistence via pcalua Launching rundll32 Control_RunDLL
Suspicious Rundll32 Executing DLL Start Export With Control Flags
Suspicious Rundll32 Execution of Timestamp-Named DLL
Suspicious Rundll32 Loading DLL from LocalAppData with Short Export (via process_creation)
Windows Rundll32 Execution Masquerading as Image Files via Image Extensions
Pivot detection · T1218.011 · 9 related

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.