Potential CVE-2021-42287 Exploitation Attempt

Status: test
Severity: medium
Log source: product windows, service system
Author: frack113
Source: github.com/SigmaHQ/sigma

The attacker creates a computer object using those permissions with a password known to her. After that she clears the attribute ServicePrincipalName on the computer object. Because she created the object (CREATOR OWNER), she gets granted additional permissions and can do many changes to the object.

MITRE ATT&CK coverage

Tactic	Techniques
Credential Access	`T1558.003` Steal or Forge Kerberos Tickets: Kerberoasting

Telemetry coverage

Provider	Record / event type
Directory-Services-SAM	Event ID 16990: The security account manager blocked a non-administrator from creating an Active Directory account in this domain with mismatched objectClass and u...
Directory-Services-SAM	Event ID 16991: The security account manager blocked a non-administrator from creating or renaming a computer account using an invalid sAMAccountName.

Rule body

title: Potential CVE-2021-42287 Exploitation Attempt
id: e80a0fee-1a62-4419-b31e-0d0db6e6013a
related:
    - id: 44bbff3e-4ca3-452d-a49a-6efa4cafa06f
      type: similar
status: test
description: |
    The attacker creates a computer object using those permissions with a password known to her.
    After that she clears the attribute ServicePrincipalName on the computer object.
    Because she created the object (CREATOR OWNER), she gets granted additional permissions and can do many changes to the object.
references:
    - https://cloudbrothers.info/en/exploit-kerberos-samaccountname-spoofing/
author: frack113
date: 2021-12-15
modified: 2023-04-14
tags:
    - attack.credential-access
    - attack.t1558.003
    - detection.emerging-threats
    - cve.2021-42287
logsource:
    product: windows
    service: system
detection:
    selection:
        Provider_Name: Microsoft-Windows-Directory-Services-SAM  # Active Directory
        EventID:
            - 16990 # Object class and UserAccountControl validation failure
            - 16991 # SAM Account Name validation failure
    condition: selection
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

selection

Stage 1: `selection`

selection:
    Provider_Name: Microsoft-Windows-Directory-Services-SAM
    EventID:
        - 16990
        - 16991

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Provider_Name`	eq	`Microsoft-Windows-Directory-Services-SAM`	`field:"Provider_Name" kind:eq value:"Microsoft-Windows-Directory-Services-SAM"`