Detect Verclsid in Splunk
Adversaries may abuse verclsid.exe to proxy execution of malicious code. Verclsid.exe (Extension CLSID Verification Host) is responsible for verifying each shell extension before it is used by Windows Explorer or the Windows Shell. Adversaries can register a malicious COM object under a CLSID and then invoke verclsid.exe with that CLSID to trigger execution. Since verclsid.exe is signed by Microsoft and performs legitimate COM verification activities, it can bypass application control solutions. Hancitor malware is a known user of this technique.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1218 System Binary Proxy Execution
- Sub-technique
- T1218.012 Verclsid
- Canonical reference
- https://attack.mitre.org/techniques/T1218/012/
SPL Detection Query
index=wineventlog sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode=1
(Image="*\\verclsid.exe" OR ParentImage="*\\verclsid.exe")
| eval HasCLSID=if(match(CommandLine, "\{[0-9A-Fa-f]{8}-[0-9A-Fa-f]{4}"), 1, 0)
| eval SuspiciousParent=if(match(ParentImage, "(cmd|powershell|wscript|cscript|mshta|winword|excel|outlook)\.exe"), 1, 0)
| eval ForcedExec=if(match(CommandLine, "(/s|/c)"), 1, 0)
| eval SuspiciousChild=if(ParentImage="*\\verclsid.exe" AND match(Image, "(cmd|powershell|wscript|cscript)\.exe"), 1, 0)
| eval RiskScore=HasCLSID + SuspiciousParent + ForcedExec + SuspiciousChild
| where RiskScore > 1 OR SuspiciousChild=1
| table _time, host, User, Image, CommandLine, ParentImage, ParentCommandLine, HasCLSID, SuspiciousParent, ForcedExec, SuspiciousChild, RiskScore
| sort - _timeDetects verclsid.exe abuse using Sysmon Event ID 1. Requires at least a risk score of 2 to reduce noise from legitimate Windows shell verification activity. Child process spawning from verclsid.exe is unconditionally flagged as highly suspicious.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Windows Explorer and shell initialization processes that invoke verclsid.exe to verify shell extensions
- Software that registers COM shell extensions during installation
- Security software using verclsid.exe for COM extension auditing
- Administrators manually verifying CLSID registrations
Other platforms for T1218.012
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Verclsid Execution with CLSID Argument
Expected signal: Sysmon Event ID 1: verclsid.exe with /S /C and CLSID in command line. Security Event ID 4688. The process will attempt to load the COM object registered for this CLSID.
- Test 2Verclsid Launched from cmd.exe
Expected signal: Sysmon Event ID 1: cmd.exe then verclsid.exe with ParentImage=cmd.exe. HasCLSID, ForcedExec, and SuspiciousParent all fire.
- Test 3Malicious COM CLSID Registration for Verclsid Abuse
Expected signal: Sysmon Event ID 13 (Registry Value Set): HKCU\Software\Classes\CLSID path with Temp DLL path as data. The COM registration hunting query captures this as a malicious InprocServer32 pointing to a temp directory.
References (5)
- https://attack.mitre.org/techniques/T1218/012/
- https://lolbas-project.github.io/lolbas/Binaries/Verclsid/
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.012/T1218.012.md
- https://www.winosbit.com/articles/what-is-verclsid.exe
- https://www.proofpoint.com/us/threat-insight/post/hancitor-goes-dark
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