User Added To Highly Privileged Group

Severity: high
Author: Nasreddine Bencherchali (Nextron Systems)
Source: upstream

Detects addition of users to highly privileged groups via "Net" or "Add-LocalGroupMember".

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1098` Account Manipulation
Privilege Escalation	`T1098` Account Manipulation

Event coverage

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

Stages and Predicates

Stage 1: `all of selection_main`

or:
CommandLine|contains: ' -Group '
CommandLine|contains: 'Add-LocalGroupMember '
CommandLine|contains: ' /add'
CommandLine|contains: 'localgroup '

Stage 2: `all of selection_group`

or:
CommandLine|contains: 'Group Policy Creator Owners'
CommandLine|contains: 'Schema Admins'

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	`-Group` corpus 3 (sigma 3) `/add` corpus 5 (sigma 5) `Add-LocalGroupMember` corpus 3 (sigma 3) `Group Policy Creator Owners` `Schema Admins` `localgroup` corpus 3 (sigma 3)