Uncommon Child Process Of AddinUtil.EXE

Severity: medium
Author: Michael McKinley (@McKinleyMike), Tony Latteri (@TheLatteri)
Source: upstream

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
Defense Evasion	`T1218` System Binary Proxy Execution

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation
Security-Auditing	4688	A new process has been created.

Stages and Predicates

Stage 1: `selection`

ParentImage|endswith: '\addinutil.exe'

Stage 2: `not 1 of filter_main_werfault`

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

Field	Kind	Values
`Image`	ends_with	`:\Windows\SysWOW64\werfault.exe` `:\Windows\System32\conhost.exe` corpus 2 (sigma 2) `:\Windows\System32\werfault.exe`
`ParentImage`	ends_with	`\addinutil.exe`