huntrule

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
AnalysisDetection

ATT&CK techniques

Cred Access

  1. Recon

  2. Resource Dev

  3. Initial Access

  4. Execution

  5. Persistence

  6. Priv Esc

  7. Defense Evasion

  8. Cred Access

  9. Discovery

  10. Lateral Movement

  11. Collection

  12. C2

  13. Exfiltration

  14. 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

Related detections9 linkedT1558.003 — drag to rearrange
Malicious Kerberos Ticket File Creation Indicating Credential Theft (via file_event)
Suspicious Kerberoasting via setspn Service Principal Query
Masquerading Kerberos Ticket Abuse via Rubeus (via process_creation)
Possible Targeted Kerberoasting via servicePrincipalName Modification
Suspicious SQL Service Principal Name Enumeration via Setspn
Windows: Suspicious Kerberos Ticket Requests from PowerShell Using KerberosRequestorSecurityToken
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
  1. v5
    Candidate ingested via manual entry.2026-07-31
  2. v4
    Candidate ingested via manual entry.2026-07-31
  3. v3
    Candidate ingested via manual entry.2026-07-31
  4. v2
    Candidate ingested via manual entry.2026-07-31
  5. 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.