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Detection rules › Sigma

Suspicious Eventlog Clear

Status
test
Severity
medium
Log source
product windows, category ps_script
Author
Nasreddine Bencherchali (Nextron Systems), Swachchhanda Shrawan Poudel (Nextron Systems)
Source
github.com/SigmaHQ/sigma

Detects usage of known powershell cmdlets such as "Clear-EventLog" to clear the Windows event logs

MITRE ATT&CK coverage

TacticTechniques
Defense ImpairmentT1685.005 Disable or Modify Tools: Clear Windows Event Logs

Event coverage

ProviderEventTitle
PowerShellEvent ID 4104Creating Scriptblock text (MessageNumber of MessageTotal).

Rule body yaml

title: Suspicious Eventlog Clear
id: 0f017df3-8f5a-414f-ad6b-24aff1128278
related:
    - id: cc36992a-4671-4f21-a91d-6c2b72a2edf5
      type: derived
status: test
description: Detects usage of known powershell cmdlets such as "Clear-EventLog" to clear the Windows event logs
references:
    - https://twitter.com/oroneequalsone/status/1568432028361830402
    - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1070.001/T1070.001.md
    - https://eqllib.readthedocs.io/en/latest/analytics/5b223758-07d6-4100-9e11-238cfdd0fe97.html
    - https://stackoverflow.com/questions/66011412/how-to-clear-a-event-log-in-powershell-7
    - https://learn.microsoft.com/en-us/dotnet/api/system.diagnostics.eventing.reader.eventlogsession.clearlog?view=windowsdesktop-9.0&viewFallbackFrom=dotnet-plat-ext-5.0#System_Diagnostics_Eventing_Reader_EventLogSession_ClearLog_System_String_
    - https://learn.microsoft.com/en-us/dotnet/api/system.diagnostics.eventlog.clear
author: Nasreddine Bencherchali (Nextron Systems), Swachchhanda Shrawan Poudel (Nextron Systems)
date: 2022-09-12
modified: 2025-10-06
tags:
    - attack.defense-impairment
    - attack.t1685.005
logsource:
    product: windows
    category: ps_script
    definition: 'Requirements: Script Block Logging must be enabled'
detection:
    selection:
        - ScriptBlockText|contains:
              - 'Clear-EventLog '
              - 'Remove-EventLog '
              - 'Limit-EventLog '
              - 'Clear-WinEvent '
        - ScriptBlockText|contains|all:
              - 'Eventing.Reader.EventLogSession' # [System.Diagnostics.Eventing.Reader.EventLogSession]::GlobalSession.ClearLog($_.LogName)
              - 'ClearLog'
        - ScriptBlockText|contains|all:
              - 'Diagnostics.EventLog'
              - 'Clear'
    condition: selection
falsepositives:
    - Rare need to clear logs before doing something. Sometimes used by installers or cleaner scripts. The script should be investigated to determine if it's legitimate
level: medium

Stages and Predicates

Stage 0: condition

selection

Stage 1: selection

selection:
    - ScriptBlockText|contains:
          - 'Clear-EventLog '
          - 'Remove-EventLog '
          - 'Limit-EventLog '
          - 'Clear-WinEvent '
    - ScriptBlockText|contains|all:
          - 'Eventing.Reader.EventLogSession'
          - 'ClearLog'
    - ScriptBlockText|contains|all:
          - 'Diagnostics.EventLog'
          - 'Clear'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
ScriptBlockTextmatch
  • Clear
  • Clear-EventLog
  • Clear-WinEvent
  • ClearLog corpus 2 (sigma 2)
  • Diagnostics.EventLog
  • Eventing.Reader.EventLogSession
  • Limit-EventLog
  • Remove-EventLog