huntrule

Windows Regsvr32.exe Executed with Suspicious File Extension Masquerading as DLL

Alerts when REGSVR32.exe runs with a command-line argument ending in a suspicious masquerade file extension.

FreeReviewedSigma · High · v1
Product
windows
Category
process_creation
Author
Florian Roth (Nextron Systems), frack113 (SigmaHQ), DRL 1.1
Published
2021-11-29
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 REGSVR32.exe is executed and the command line ends with one of several file extensions commonly used for masquerading. Attackers may abuse regsvr32 to load a DLL via a crafted argument while disguising the payload filename with a benign-looking extension. The detection relies on Windows process creation telemetry, including the executable image/filename and the full command line suffix.

Reporting behind it

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Suspicious Run Key Persistence Executing regsvr32
Suspicious regsvr32 Registering DLL from User AppData
Malicious Regsvr32 Loading Masqueraded VPN DLL via Process Creation
Malicious Regsvr32 ShellExec_RunDLL Proxy Execution (via process_creation)
Suspicious DLL Execution via Regsvr32 DllInstall of dat File
Windows Regsvr32.exe Executed with Suspicious File Extension Masquerading as DLL
Pivot detection · T1218.010 · 9 related

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