Kerberos pre-authentication failed
Kerberos pre-authentication verification failed (`bad password or AS-REP Roasting attempt`).
Event ID 4771 is generated on Domain Controllers when a user enters an incorrect password during initial pre-authentication (`Failure Code: 0x18`). If an account has `Do not require Kerberos preauthentication` (`UF_DONT_REQUIRE_PREAUTH`) enabled, attackers request TGT hashes directly without a password—known as **AS-REP Roasting**.
Failure Reason / Root Cause:
User mistyping domain password, brute-force attacks, or AS-REP Roasting attempts against vulnerable accounts.
Raw Event XML snippet
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
<System>
<Provider Name="Microsoft-Windows-Security-Auditing" Guid="{54849625-5478-4994-A5BA-3E3B0328C30D}" />
<EventID>4771</EventID>
<Version>0</Version>
<Level>0</Level>
<Task>12544</Task>
<Opcode>0</Opcode>
<Keywords>0x8020000000000000</Keywords>
<TimeCreated SystemTime="2026-07-17T09:54:44.909Z" />
<EventRecordID>1048576</EventRecordID>
<Correlation />
<Execution ProcessID="612" ThreadID="1024" />
<Channel>Security</Channel>
<Computer>DC01.enterprise.internal</Computer>
<Security />
</System>
<EventData>
<Data Name="SubjectUserSid">S-1-5-18</Data>
<Data Name="SubjectUserName">SYSTEM</Data>
<Data Name="SubjectDomainName">NT AUTHORITY</Data>
<Data Name="SubjectLogonId">0x3e7</Data>
<!-- Event telemetry fields specific to Kerberos pre-authentication failed -->
</EventData>
</Event>MITRE ATT&CK mapping
| ID | Technique | Tactic |
|---|---|---|
T1558.004 | Steal or Forge Kerberos Tickets: AS-REP Roasting | Credential Access |
T1110 | Brute Force | Credential Access |
Recommended actions
- Audit Active Directory to identify and disable `Do not require Kerberos preauthentication` on all user accounts (`prevent AS-REP Roasting`).
- Correlate spikes in Event 4771 (`Failure Code: 0x18`) with Event 4625 across external gateway IP ranges.