AddinUtil.EXE Execution From Uncommon Directory

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

Detects execution of the Add-In deployment cache updating utility (AddInutil.exe) from a non-standard directory.

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: `selection`

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

Stage 2: `not 1 of filter_main_legit_location`

or:
Image|contains: ':\Windows\Microsoft.NET\Framework64\'
Image|contains: ':\Windows\Microsoft.NET\FrameworkArm64\'
Image|contains: ':\Windows\Microsoft.NET\FrameworkArm\'
Image|contains: ':\Windows\Microsoft.NET\Framework\'
Image|contains: ':\Windows\WinSxS\'

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	`\addinutil.exe` corpus 4 (sigma 4)
`Image`	match	`:\Windows\Microsoft.NET\Framework64\` corpus 3 (sigma 3) `:\Windows\Microsoft.NET\FrameworkArm64\` corpus 3 (sigma 3) `:\Windows\Microsoft.NET\FrameworkArm\` corpus 3 (sigma 3) `:\Windows\Microsoft.NET\Framework\` corpus 3 (sigma 3) `:\Windows\WinSxS\` corpus 3 (sigma 3)
`OriginalFileName`	eq	`AddInUtil.exe` corpus 3 (sigma 3)