Potential AMSI COM Server Hijacking
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About the rule
Rule Type
Standard
Rule Description
Detects changes to the AMSI come server registry key in order disable AMSI scanning functionalities. When AMSI attempts to starts its COM component, it will query its registered CLSID and return a non-existent COM server. This causes a load failure and prevents any scanning methods from being accessed, ultimately rendering AMSI useless
Severity
Trouble
Rule Requirement
Criteria
Action1: actionname = "Registry value modified" AND (OBJECTNAME endswith "\CLSID\{fdb00e52-a214-4aa1-8fba-4357bb0072ec}\InProcServer32\(Default)" OR (OBJECTNAME endswith "\CLSID\{fdb00e52-a214-4aa1-8fba-4357bb0072ec}\InProcServer32" AND OBJECTVALUENAME = "(Default)")) AND INFORMATION != "%windir%\system32\amsi.dll" select Action1.HOSTNAME,Action1.MESSAGE,Action1.OBJECTNAME,Action1.PROCESSNAME,Action1.PREVVAL,Action1.CHANGES
Detection
Execution Mode
realtime
Log Sources
Windows
Author
Nasreddine Bencherchali (Nextron Systems)
