Windows Directory Services: CVE-2021-42287 SAMAccountName spoofing validation failures

Looks for Directory Services SAM validation failures (Event 16990/16991) that may indicate CVE-2021-42287 exploitation attempts.

FreeReviewedSigma · Medium · v5

Product: windows
Service: system
Author: frack113 (SigmaHQ), DRL 1.1
Published: 2021-12-15
Updated: 2026-07-31

Analysis Detection

ATT&CK techniques

Cred Access

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
- T1558.003Kerberoasting
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule flags Windows Directory Services System events indicating validation failures for object class and UserAccountControl and for SAM account name. Such errors can occur during attempts to create or manipulate computer objects in Active Directory in a way consistent with SAMAccountName spoofing behavior tied to CVE-2021-42287. It relies on Microsoft-Windows-Directory-Services-SAM telemetry and the specific event IDs 16990 and 16991.

Reporting behind it

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Windows Process Creation: RemoteKrbRelay Kerberos Relay Tool Execution

Windows Kerberos KDC Key Distribution Failure: No Suitable Encryption Key or Unsupported EType

Rubeus HackTool Execution via PowerShell ScriptBlock Flags (Windows)

Windows Directory Services: CVE-2021-42287 SAMAccountName spoofing validation failures

Pivot detection · T1558.003 · 9 related

Changelog

v5
Candidate ingested via manual entry.2026-07-31
v4
Candidate ingested via manual entry.2026-07-31
v3
Candidate ingested via manual entry.2026-07-31
v2
Candidate ingested via manual entry.2026-07-31
v1
No changelog recorded for this version.2026-07-30

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

windows-directory-services-sam-account-name-validation-failures-indicative-of-cv-e80a0fee

title: "Windows Directory Services: CVE-2021-42287 SAMAccountName spoofing validation failures"
id: e3a80b2b-8dba-4a02-a5fb-0a55bfaac9eb
related:
  - id: 44bbff3e-4ca3-452d-a49a-6efa4cafa06f
    type: similar
  - id: e80a0fee-1a62-4419-b31e-0d0db6e6013a
    type: derived
status: test
description: This rule flags Windows Directory Services System events indicating validation failures for object class and UserAccountControl and for SAM account name. Such errors can occur during attempts to create or manipulate computer objects in Active Directory in a way consistent with SAMAccountName spoofing behavior tied to CVE-2021-42287. It relies on Microsoft-Windows-Directory-Services-SAM telemetry and the specific event IDs 16990 and 16991.
references:
  - https://cloudbrothers.info/en/exploit-kerberos-samaccountname-spoofing/
  - https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2021/Exploits/CVE-2021-42287/win_system_exploit_cve_2021_42287.yml
author: frack113, Huntrule Team
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
    EventID:
      - 16990
      - 16991
  condition: selection
falsepositives:
  - Unknown
level: medium
license: DRL-1.1

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