huntrule

Windows rundll32 Execution With Uncommon DLL/CPL/INF Extension in Command Line

Alerts on Windows rundll32 executions whose command lines lack common .cpl/.dll/.inf endings, indicating potential unusual invocation.

FreeReviewedSigma · Medium · v1
Product
windows
Category
process_creation
Author
Tim Shelton, Florian Roth (Nextron Systems), Yassine Oukessou (SigmaHQ), DRL 1.1
Published
2022-01-13
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 flags process creation events where rundll32.exe is executed and the command line does not include common extension endings such as .cpl, .dll, or .inf (with various quoting and delimiter patterns). Attackers may use unusual extension handling with rundll32 to blend in while still invoking code paths via specific DLL-style arguments. The detection relies on process creation telemetry including Image/OriginalFileName and CommandLine content, with exclusions for null/empty command lines and several known benign parent-child patterns.

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 With Uncommon DLL/CPL/INF Extension in Command Line
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.