New DLL Added to AppInit_DLLs Registry Key

Status: test
Severity: medium
Log source: category registry_event, product windows
Author: Ilyas Ochkov, oscd.community, Tim Shelton
Source: github.com/SigmaHQ/sigma

DLLs that are specified in the AppInit_DLLs value in the Registry key HKLM\Software\Microsoft\Windows NT\CurrentVersion\Windows are loaded by user32.dll into every process that loads user32.dll

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1546.010` Event Triggered Execution: AppInit DLLs
Privilege Escalation	`T1546.010` Event Triggered Execution: AppInit DLLs

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 12: RegistryEvent (Object create and delete)
Sysmon	Event ID 13: RegistryEvent (Value Set)
Sysmon	Event ID 14: RegistryEvent (Key and Value Rename)

Rule body

title: New DLL Added to AppInit_DLLs Registry Key
id: 4f84b697-c9ed-4420-8ab5-e09af5b2345d
status: test
description: DLLs that are specified in the AppInit_DLLs value in the Registry key HKLM\Software\Microsoft\Windows NT\CurrentVersion\Windows are loaded by user32.dll into every process that loads user32.dll
references:
    - https://eqllib.readthedocs.io/en/latest/analytics/822dc4c5-b355-4df8-bd37-29c458997b8f.html
author: Ilyas Ochkov, oscd.community, Tim Shelton
date: 2019-10-25
modified: 2022-12-25
tags:
    - attack.privilege-escalation
    - attack.persistence
    - attack.t1546.010
logsource:
    category: registry_event
    product: windows
detection:
    selection:
        - TargetObject|endswith:
              - '\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls'
              - '\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls'
        # Key Rename
        - NewName|endswith:
              - '\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls'
              - '\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls'
    filter:
        Details: '(Empty)'
    condition: selection and not filter
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not filter

Stage 1: `selection`

selection:
    - TargetObject|endswith:
          - '\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls'
          - '\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls'
    - NewName|endswith:
          - '\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls'
          - '\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls'

Stage 2: `not filter`

filter:
    Details: '(Empty)'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`Details`	eq	`(Empty)`	`excludes:Details` `field:"Details" value:"(Empty)"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`NewName`	ends_with	`\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls` `\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls`	`field:"NewName" kind:ends_with`
`TargetObject`	ends_with	`\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls` `\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls`	`field:"TargetObject" kind:ends_with`