Explorer NOUACCHECK Flag

Hunt Hypothesis

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

Detection Rule

Sigma (Original)

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

KQL (Azure Sentinel)

imProcessCreate
| where (TargetProcessName endswith "\\explorer.exe" and TargetProcessCommandLine contains "/NOUACCHECK") and (not((ActingProcessCommandLine =~ "C:\\Windows\\system32\\svchost.exe -k netsvcs -p -s Schedule" or (ParentProcessName =~ "C:\\Windows\\System32\\svchost.exe" or ActingProcessName =~ "C:\\Windows\\System32\\svchost.exe"))))

Required Data Sources

False Positive Guidance

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

MITRE ATT&CK Context

• Tactic: Privilege Escalation
• Technique: T1548.002 — T1548.002

References

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