Uncommon Child Process Of AddinUtil.EXE

Status: test
Severity: medium
Log source: category process_creation, product windows
Author: Michael McKinley (@McKinleyMike), Tony Latteri (@TheLatteri)
Source: github.com/SigmaHQ/sigma

Detects uncommon child processes of the Add-In deployment cache updating utility (AddInutil.exe) which could be a sign of potential abuse of the binary to proxy execution via a custom Addins.Store payload.

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1218` System Binary Proxy Execution

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation
Security-Auditing	Event ID 4688: A new process has been created.

Rule body

title: Uncommon Child Process Of AddinUtil.EXE
id: b5746143-59d6-4603-8d06-acbd60e166ee
status: test
description: |
    Detects uncommon child processes of the Add-In deployment cache updating utility (AddInutil.exe) which could be a sign of potential abuse of the binary to proxy execution via a custom Addins.Store payload.
references:
    - https://www.blue-prints.blog/content/blog/posts/lolbin/addinutil-lolbas.html
author: Michael McKinley (@McKinleyMike), Tony Latteri (@TheLatteri)
date: 2023-09-18
tags:
    - attack.stealth
    - attack.t1218
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        ParentImage|endswith: '\addinutil.exe'
    filter_main_werfault:
        Image|endswith:
            - ':\Windows\System32\conhost.exe'
            - ':\Windows\System32\werfault.exe'
            - ':\Windows\SysWOW64\werfault.exe'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_*

Stage 1: `selection`

selection:
    ParentImage|endswith: '\addinutil.exe'

Stage 2: `not filter_main_werfault`

filter_main_werfault:
    Image|endswith:
        - ':\Windows\System32\conhost.exe'
        - ':\Windows\System32\werfault.exe'
        - ':\Windows\SysWOW64\werfault.exe'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`Image`	ends_with	`:\Windows\SysWOW64\werfault.exe`	`excludes:Image` `field:"Image" value:":\Windows\SysWOW64\werfault.exe"`
`Image`	ends_with	`:\Windows\System32\conhost.exe`	`excludes:Image` `field:"Image" value:":\Windows\System32\conhost.exe"`
`Image`	ends_with	`:\Windows\System32\werfault.exe`	`excludes:Image` `field:"Image" value:":\Windows\System32\werfault.exe"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`ParentImage`	ends_with	`\addinutil.exe`	`field:"ParentImage" kind:ends_with value:"\addinutil.exe"`