Abuse of Regsvcs.exe or Regasm.exe to execute arbitrary code embedded in .NET assemblies via [ComRegisterFunction]/[ComUnregisterFunction]. Behavioral chain: (1) Process creation of regsvcs/regasm with suspicious assembly paths/flags → (2) Assembly/DLL load inside regsvcs/regasm → (3) Registry writes to HKCR\CLSID/ProgID during COM registration → (4) Optional child process or network activity spawned by installer/registration code.
WinEventLog:Security
EventCode=4688
WinEventLog:Sysmon
EventCode=7
WinEventLog:Sysmon
EventCode=12
WinEventLog:Sysmon
EventCode=13, 14
WinEventLog:Sysmon
EventCode=11
WinEventLog:PowerShell
EventCode=4103, 4104, 4105, 4106
WinEventLog:Sysmon
EventCode=3, 22
[AssemblyPathRegex]
Environment-specific paths to flag (e.g., %TEMP%, Downloads, OneDrive, SMB shares). Helps suppress known-good installers.
[SuspiciousFlags]
Arguments like /unregister (/u), /codebase, /regfile which may indicate abuse. Tune per enterprise use of regasm/regsvcs.
[ParentProcessAllowList]
Legitimate parents (e.g., setup.exe, msiexec.exe). Analyst can prune false positives from Office or script hosts.
[KnownGoodAssemblies]
Hashes or publisher info for approved assemblies commonly registered in the environment.
[RegistryKeyAllowList]
Approved CLSIDs/ProgIDs written during sanctioned software installs.
[TimeWindow]
Correlation window (e.g., 5–10 min) between file drop → regasm/regsvcs exec → registry writes → child activity.
[SignedToUnsignedTransition]
Alert if Microsoft-signed regasm/regsvcs loads or triggers unsigned assemblies/children.