Uncommon AddinUtil.EXE CommandLine Execution

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

Detects execution of the Add-In deployment cache updating utility (AddInutil.exe) with uncommon Addinroot or Pipelineroot paths. An adversary may execute AddinUtil.exe with uncommon Addinroot/Pipelineroot paths that point to the adversaries 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

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\addinutil.exe'
OriginalFileName: AddInUtil.exe

Stage 2: `all of selection_cli`

or:
CommandLine|contains: '-AddInRoot:'
CommandLine|contains: '-PipelineRoot:'

Stage 3: `not 1 of filter_main_addinroot`

or:
CommandLine|contains: '-AddInRoot:C:\Program Files (x86)\Common Files\Microsoft Shared\VSTA'
CommandLine|contains: '-AddInRoot:"C:\Program Files (x86)\Common Files\Microsoft Shared\VSTA'
CommandLine|contains: '-PipelineRoot:C:\Program Files (x86)\Common Files\Microsoft Shared\VSTA'
CommandLine|contains: '-PipelineRoot:"C:\Program Files (x86)\Common Files\Microsoft Shared\VSTA'

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
`CommandLine`	match	`-AddInRoot:` corpus 2 (sigma 2) `-AddInRoot:"C:\Program Files (x86)\Common Files\Microsoft Shared\VSTA` `-AddInRoot:C:\Program Files (x86)\Common Files\Microsoft Shared\VSTA` `-PipelineRoot:` corpus 2 (sigma 2) `-PipelineRoot:"C:\Program Files (x86)\Common Files\Microsoft Shared\VSTA` `-PipelineRoot:C:\Program Files (x86)\Common Files\Microsoft Shared\VSTA`
`Image`	ends_with	`\addinutil.exe` corpus 4 (sigma 4)
`OriginalFileName`	eq	`AddInUtil.exe` corpus 3 (sigma 3)