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Detection rules › Sigma

Potentially Suspicious Child Process Of Regsvr32

Status
test
Severity
high
Log source
category process_creation, product windows
Author
elhoim, Florian Roth (Nextron Systems), Nasreddine Bencherchali (Nextron Systems)
Source
github.com/SigmaHQ/sigma

Detects potentially suspicious child processes of "regsvr32.exe".

Known false positives

  • Unlikely, but can rarely occur. Apply additional filters accordingly.

MITRE ATT&CK coverage

TacticTechniques
Stealth

Telemetry coverage

ProviderRecord / event type
SysmonEvent ID 1: Process creation
Security-AuditingEvent ID 4688: A new process has been created.

Rule body

title: Potentially Suspicious Child Process Of Regsvr32
id: 6f0947a4-1c5e-4e0d-8ac7-53159b8f23ca
related:
    - id: 8e2b24c9-4add-46a0-b4bb-0057b4e6187d
      type: obsolete
status: test
description: Detects potentially suspicious child processes of "regsvr32.exe".
references:
    - https://redcanary.com/blog/intelligence-insights-april-2022/
    - https://www.echotrail.io/insights/search/regsvr32.exe
    - https://www.ired.team/offensive-security/code-execution/t1117-regsvr32-aka-squiblydoo
author: elhoim, Florian Roth (Nextron Systems), Nasreddine Bencherchali (Nextron Systems)
date: 2022-05-05
modified: 2023-05-26
tags:
    - attack.stealth
    - attack.t1218.010
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        ParentImage|endswith: '\regsvr32.exe'
        Image|endswith:
            - '\calc.exe'
            - '\cscript.exe'
            - '\explorer.exe'
            - '\mshta.exe'
            - '\net.exe'
            - '\net1.exe'
            - '\nltest.exe'
            - '\notepad.exe'
            - '\powershell.exe'
            - '\pwsh.exe'
            - '\reg.exe'
            - '\schtasks.exe'
            - '\werfault.exe'
            - '\wscript.exe'
    filter_main_werfault:
        Image|endswith: '\werfault.exe'
        CommandLine|contains: ' -u -p '
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unlikely, but can rarely occur. Apply additional filters accordingly.
level: high

Stages and Predicates

Stage 0: condition

selection and not 1 of filter_main_*

Stage 1: selection

selection:
    ParentImage|endswith: '\regsvr32.exe'
    Image|endswith:
        - '\calc.exe'
        - '\cscript.exe'
        - '\explorer.exe'
        - '\mshta.exe'
        - '\net.exe'
        - '\net1.exe'
        - '\nltest.exe'
        - '\notepad.exe'
        - '\powershell.exe'
        - '\pwsh.exe'
        - '\reg.exe'
        - '\schtasks.exe'
        - '\werfault.exe'
        - '\wscript.exe'

Stage 2: not filter_main_werfault

filter_main_werfault:
    Image|endswith: '\werfault.exe'
    CommandLine|contains: ' -u -p '

Exclusions

The rule actively suppresses these predicates.

FieldKindExcluded valuesSearch
CommandLinematch -u -p excludes:CommandLine field:"CommandLine" value:" -u -p "
Imageends_with\werfault.exeexcludes:Image field:"Image" value:"\werfault.exe"

Indicators

These rows show field, operator, and value matches.

FieldKindValuesSearch
Imageends_with
  • \calc.exe corpus 14 (sigma 14)
  • \cscript.exe corpus 72 (sigma 72)
  • \explorer.exe corpus 13 (sigma 13)
  • \mshta.exe corpus 66 (sigma 66)
  • \net.exe corpus 49 (sigma 49)
  • \net1.exe corpus 47 (sigma 47)
  • \nltest.exe corpus 9 (sigma 9)
  • \notepad.exe corpus 10 (sigma 10)
  • \powershell.exe corpus 179 (sigma 178, kusto 1)
  • \pwsh.exe corpus 165 (sigma 164, kusto 1)
  • \reg.exe corpus 58 (sigma 58)
  • \schtasks.exe corpus 55 (sigma 55)
  • \werfault.exe corpus 8 (sigma 8)
  • \wscript.exe corpus 74 (sigma 74)
field:"Image" kind:ends_with
ParentImageends_with
  • \regsvr32.exe corpus 11 (sigma 11)
field:"ParentImage" kind:ends_with value:"\regsvr32.exe"