Detect Clear Windows Event Logs in CrowdStrike LogScale
Adversaries clear Windows Event Logs to remove evidence of intrusion activity. Primary methods include the wevtutil command-line utility (wevtutil cl system/security/application), the PowerShell Remove-EventLog cmdlet, the Windows Event Viewer GUI, and direct deletion of .evtx log files from C:\Windows\System32\winevt\logs\. When a log is cleared, Windows generates Event ID 1102 (Security log cleared) in the Security log and Event ID 104 (System log cleared) in the System log — but these disappear if the generating log is also cleared. APT28, APT38, APT41, Volt Typhoon, LockBit 2.0/3.0, RansomHub, NotPetya, Olympic Destroyer, BlackCat, and many others routinely clear event logs as post-compromise cleanup.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1070 Indicator Removal
- Sub-technique
- T1070.001 Clear Windows Event Logs
- Canonical reference
- https://attack.mitre.org/techniques/T1070/001/
LogScale Detection Query
(
#event_simpleName in [ProcessRollup2, SyntheticProcessRollup2]
| FileName = "wevtutil.exe"
| CommandLine = /\b(cl|clear-log|clear)\b/i
| DetectionType := "WevtutilClear"
)
| union (
#event_simpleName in [ProcessRollup2, SyntheticProcessRollup2]
| FileName = /powershell(ise)?\.exe/i
| CommandLine = /(Remove-EventLog|Clear-EventLog)/i
| DetectionType := "PowerShellClear"
)
| table([_time, ComputerName, UserName, FileName, CommandLine, DetectionType])
| sort(_time, order=desc, limit=200)Detects Windows Event Log clearing in CrowdStrike Falcon LogScale by querying ProcessRollup2 and SyntheticProcessRollup2 events for two detection branches: wevtutil.exe invocations with clear-family command arguments (cl, clear-log, clear), and PowerShell or PowerShell ISE processes executing Remove-EventLog or Clear-EventLog cmdlets. Results are unioned and labeled with DetectionType for analyst triage.
Data Sources
Required Tables
False Positives & Tuning
- CrowdStrike Falcon sensor upgrades or policy deployments that trigger automated wevtutil calls to clear diagnostic event logs
- IT automation tools such as Ansible, Chef, or Puppet clearing event logs as part of Windows workstation provisioning or hardening runbooks
- Help desk staff executing Clear-EventLog via interactive or remote PowerShell sessions to resolve event log corruption on endpoints
Other platforms for T1070.001
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 1Clear Security Event Log with wevtutil
Expected signal: Windows Event Log: Security Event ID 1102 (The audit log was cleared) generated just before the log is cleared. Sysmon Event ID 1: wevtutil.exe process creation with 'cl Security' argument. After clearing, the Security log is empty except for the Event ID 4608 (Windows is starting up) that follows a fresh log.
- Test 2Clear Multiple Event Logs Using wevtutil Loop
Expected signal: Multiple Sysmon Event ID 1 events for wevtutil.exe with different log names. Security Event ID 1102 for Security log. System Event ID 104 for each other log cleared. The for loop structure will appear in the parent cmd.exe command line.
- Test 3Clear Event Log via PowerShell Remove-EventLog
Expected signal: PowerShell process creation with Remove-EventLog command. Sysmon Event ID 13 (Registry): removal of the EventLog registry key under HKLM\SYSTEM\CurrentControlSet\Services\EventLog\ArgusTest. System Event ID 104 may be generated for the deleted log.
References (5)
- https://attack.mitre.org/techniques/T1070/001/
- https://docs.microsoft.com/windows-server/administration/windows-commands/wevtutil
- https://docs.microsoft.com/powershell/module/microsoft.powershell.management/clear-eventlog
- https://ptylu.github.io/content/report/report.html?report=25
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1070.001/T1070.001.md
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