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Detection rules › Sigma

Change Winevt Channel Access Permission Via Registry

Status
test
Severity
high
Log source
product windows, category registry_set
Author
frack113
Source
github.com/SigmaHQ/sigma

Detects tampering with the "ChannelAccess" registry key in order to change access to Windows event channel.

MITRE ATT&CK coverage

TacticTechniques
Defense ImpairmentT1685.001 Disable or Modify Tools: Disable or Modify Windows Event Log

Event coverage

ProviderEventTitle
SysmonEvent ID 13RegistryEvent (Value Set)

Rule body yaml

title: Change Winevt Channel Access Permission Via Registry
id: 7d9263bd-dc47-4a58-bc92-5474abab390c
status: test
description: Detects tampering with the "ChannelAccess" registry key in order to change access to Windows event channel.
references:
    - https://app.any.run/tasks/77b2e328-8f36-46b2-b2e2-8a80398217ab/
    - https://learn.microsoft.com/en-us/windows/win32/api/winevt/
    - https://itconnect.uw.edu/tools-services-support/it-systems-infrastructure/msinf/other-help/understanding-sddl-syntax/
author: frack113
date: 2022-09-17
modified: 2024-03-25
tags:
    - attack.defense-impairment
    - attack.t1685.001
logsource:
    category: registry_set
    product: windows
detection:
    selection:
        TargetObject|contains: '\Microsoft\Windows\CurrentVersion\WINEVT\Channels\'
        TargetObject|endswith: '\ChannelAccess'
        # Add more interesting combinations if you found them
        Details|contains:
            - '(A;;0x1;;;LA)' # Local administrator having GENERIC ALL
            - '(A;;0x1;;;SY)' # Local System having GENERIC ALL
            - '(A;;0x5;;;BA)' # Built-in administrators having GENERIC ALL and  GENERIC WRITE
    filter_main_trustedinstaller:
        Image: 'C:\Windows\servicing\TrustedInstaller.exe'
    filter_main_tiworker:
        Image|startswith: 'C:\Windows\WinSxS\'
        Image|endswith: '\TiWorker.exe'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: condition

selection and not 1 of filter_main_*

Stage 1: selection

selection:
    TargetObject|contains: '\Microsoft\Windows\CurrentVersion\WINEVT\Channels\'
    TargetObject|endswith: '\ChannelAccess'
    Details|contains:
        - '(A;;0x1;;;LA)'
        - '(A;;0x1;;;SY)'
        - '(A;;0x5;;;BA)'

Stage 2: not filter_main_*

filter_main_trustedinstaller:
    Image: 'C:\Windows\servicing\TrustedInstaller.exe'
filter_main_tiworker:
    Image|startswith: 'C:\Windows\WinSxS\'
    Image|endswith: '\TiWorker.exe'

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

FieldKindExcluded values
Imageends_with\TiWorker.exe
Imagestarts_withC:\Windows\WinSxS\
ImageeqC:\Windows\servicing\TrustedInstaller.exe

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
Detailsmatch
  • (A;;0x1;;;LA)
  • (A;;0x1;;;SY)
  • (A;;0x5;;;BA)
TargetObjectends_with
  • \ChannelAccess corpus 2 (sigma 2)
TargetObjectmatch
  • \Microsoft\Windows\CurrentVersion\WINEVT\Channels\ corpus 2 (sigma 2)