Explorer NOUACCHECK Flag — Sigma Rule

Rule metadata and linked tags

Author: Florian Roth (Nextron Systems). Source status: test; severity: high. Source dates: 2022-02-23 / 2022-04-21.

{
  "category": "process_creation",
  "product": "windows"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 0b23baaae78d9f4e331ac900c0db310354e05de5dc014b5eac171d34b791ff7f

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: Explorer NOUACCHECK Flag
id: 534f2ef7-e8a2-4433-816d-c91bccde289b
status: test
description: Detects suspicious starts of explorer.exe that use the /NOUACCHECK flag that allows to run all sub processes of that newly started explorer.exe without any UAC checks
references:
    - https://twitter.com/ORCA6665/status/1496478087244095491
author: Florian Roth (Nextron Systems)
date: 2022-02-23
modified: 2022-04-21
tags:
    - attack.privilege-escalation
    - attack.t1548.002
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\explorer.exe'
        CommandLine|contains: '/NOUACCHECK'
    filter_dc_logon:
        - ParentCommandLine: 'C:\Windows\system32\svchost.exe -k netsvcs -p -s Schedule'
        - ParentImage: 'C:\Windows\System32\svchost.exe' # coarse filter needed for ID 4688 Events
    condition: selection and not 1 of filter_*
falsepositives:
    - Domain Controller User Logon
    - Unknown how many legitimate software products use that method
level: high

Original YAML and metadata in JSON

False positives

• Domain Controller User Logon
• Unknown how many legitimate software products use that method

Source references

• https://twitter.com/ORCA6665/status/1496478087244095491