Group Membership Reconnaissance Via Whoami.EXE

Status: test
Severity: medium
Log source: category process_creation, product windows
Author: Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects the execution of whoami.exe with the /group command line flag to show group membership for the current user, account type, security identifiers (SID), and attributes.

MITRE ATT&CK coverage

Tactic	Techniques
Discovery	`T1033` System Owner/User Discovery

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation

Rule body

title: Group Membership Reconnaissance Via Whoami.EXE
id: bd8b828d-0dca-48e1-8a63-8a58ecf2644f
status: test
description: Detects the execution of whoami.exe with the /group command line flag to show group membership for the current user, account type, security identifiers (SID), and attributes.
references:
    - https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/whoami
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-02-28
tags:
    - attack.discovery
    - attack.t1033
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith: '\whoami.exe'
        - OriginalFileName: 'whoami.exe'
    selection_cli:
        CommandLine|contains:
            - ' /groups'
            - ' -groups'
    condition: all of selection_*
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_img`

selection_img:
    - Image|endswith: '\whoami.exe'
    - OriginalFileName: 'whoami.exe'

Stage 2: `selection_cli`

selection_cli:
    CommandLine|contains:
        - ' /groups'
        - ' -groups'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`-groups` `/groups`	`field:"CommandLine" kind:match`
`Image`	ends_with	`\whoami.exe` corpus 19 (sigma 19)	`field:"Image" kind:ends_with value:"\whoami.exe"`
`OriginalFileName`	eq	`whoami.exe` corpus 9 (sigma 9)	`field:"OriginalFileName" kind:eq value:"whoami.exe"`