Change Winevt Channel Access Permission Via Registry

Status: test
Severity: high
Log source: category registry_set, product windows
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

Tactic	Techniques
Defense Impairment	`T1685.001` Disable or Modify Tools: Disable or Modify Windows Event Log

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 13: RegistryEvent (Value Set)

Rule body

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

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`Image`	ends_with	`\TiWorker.exe`	`excludes:Image` `field:"Image" value:"\TiWorker.exe"`
`Image`	starts_with	`C:\Windows\WinSxS\`	`excludes:Image` `field:"Image" value:"C:\Windows\WinSxS\"`
`Image`	eq	`C:\Windows\servicing\TrustedInstaller.exe`	`excludes:Image` `field:"Image" value:"C:\Windows\servicing\TrustedInstaller.exe"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Details`	match	`(A;;0x1;;;LA)` `(A;;0x1;;;SY)` `(A;;0x5;;;BA)`	`field:"Details" kind:match`
`TargetObject`	ends_with	`\ChannelAccess` corpus 2 (sigma 2)	`field:"TargetObject" kind:ends_with value:"\ChannelAccess"`
`TargetObject`	match	`\Microsoft\Windows\CurrentVersion\WINEVT\Channels\` corpus 2 (sigma 2)	`field:"TargetObject" kind:match value:"\Microsoft\Windows\CurrentVersion\WINEVT\Channels\"`