5168 Security log · Object Access medium severity low volume

Windows Event ID 5168 — SPN check for SMB/SMB2 failed

The SPN (Service Principal Name) check for a client connection failed. May indicate relay attack or Kerberos misconfiguration.

Why event 5168 matters

NTLM relay attacks can generate SPN check failures. Tools: Responder, ntlmrelayx may generate this when relaying credentials. Multiple failures may indicate active relay attack in progress.

How to detect it

Alert: frequent SPN check failures from single source IP. Correlate with network events for relay attack indicators.

Log source
Security
Advanced Audit Policy — enable the 'Object Access' subcategory (Success and/or Failure).
Fields to pivot on
SubjectUserNameTargetUserNameLogonTypeIpAddressWorkstationName

MITRE ATT&CK mapping

Tactic Technique
Credential Access LLMNR/NBT-NS Poisoning and SMB Relay (T1557.001)

Detection queries

Starting points — adapt the log source, projected fields and thresholds for your environment.

Sentinel / Defender KQL
SecurityEvent
| where EventID == 5168   // SPN check for SMB/SMB2 failed
| project TimeGenerated, Computer, SubjectUserName, TargetUserName, LogonType, IpAddress, WorkstationName
| sort by TimeGenerated desc
Splunk SPL
index=* sourcetype="WinEventLog:Security" EventCode=5168
| stats count earliest(_time) as first_seen latest(_time) as last_seen by ComputerName
| sort - count   `# SPN check for SMB/SMB2 failed — add EventData fields: SubjectUserName, TargetUserName, LogonType, IpAddress`
Hunt event 5168 in Sentinel/Defender →
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Related Object Access events

4656 A handle to an object was requested 4657 A registry value was modified 4658 The handle to an object was closed 4660 An object was deleted 4663 An attempt was made to access an object 4665 An attempt was made to create an application client context 4670 Permissions on an object were changed 4690 An attempt was made to duplicate a handle to an object 4985 The state of a transaction has changed 5140 A network share object was accessed 5142 A network share object was added 5143 A network share object was modified

Frequently asked questions

What is Windows Event ID 5168?

SPN check for SMB/SMB2 failed. The SPN (Service Principal Name) check for a client connection failed. May indicate relay attack or Kerberos misconfiguration.

Which log records event 5168?

Event 5168 is written to the Security channel by Microsoft-Windows-Security-Auditing. Advanced Audit Policy — enable the 'Object Access' subcategory (Success and/or Failure).

What MITRE ATT&CK techniques map to event 5168?

Event 5168 is associated with: LLMNR/NBT-NS Poisoning and SMB Relay (T1557.001).

How do you detect activity around event 5168?

Alert: frequent SPN check failures from single source IP. Correlate with network events for relay attack indicators.