Suspicious Computer Account Name Change CVE-2021-42287

Status: test
Severity: high
Log source: product windows, service security
Author: Florian Roth (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects the renaming of an existing computer account to a account name that doesn't contain a $ symbol as seen in attacks against CVE-2021-42287

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1098` Account Manipulation
Privilege Escalation	`T1098` Account Manipulation
Stealth	`T1036` Masquerading

Telemetry coverage

Provider	Record / event type
Security-Auditing	Event ID 4781: The name of an account was changed.

Rule body

title: Suspicious Computer Account Name Change CVE-2021-42287
id: 45eb2ae2-9aa2-4c3a-99a5-6e5077655466
status: test
description: Detects the renaming of an existing computer account to a account name that doesn't contain a $ symbol as seen in attacks against CVE-2021-42287
references:
    - https://medium.com/@mvelazco/hunting-for-samaccountname-spoofing-cve-2021-42287-and-domain-controller-impersonation-f704513c8a45
author: Florian Roth (Nextron Systems)
date: 2021-12-22
modified: 2022-12-25
tags:
    - attack.privilege-escalation
    - attack.persistence
    - attack.stealth
    - attack.t1036
    - attack.t1098
    - cve.2021-42287
    - detection.emerging-threats
logsource:
    product: windows
    service: security
detection:
    selection:
        EventID: 4781 # rename user
        OldTargetUserName|contains: '$'
    filter:
        NewTargetUserName|contains: '$'
    condition: selection and not filter
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

selection and not filter

Stage 1: `selection`

selection:
    EventID: 4781
    OldTargetUserName|contains: '$'

Stage 2: `not filter`

filter:
    NewTargetUserName|contains: '$'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`NewTargetUserName`	match	`$`	`excludes:NewTargetUserName` `field:"NewTargetUserName" value:"$"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`OldTargetUserName`	match	`$`	`field:"OldTargetUserName" kind:match value:"$"`