Handling Kerberos Errors in SMB Client Authentication

Question

Handling Kerberos Errors in SMB Client Authentication

E-8437 21

Hi,

We are seeking clarification on how our SMB client should handle various Kerberos errors encountered during authentication.

The MS-KILE specification provides guidance on recovering from KRB_AP_ERR_SKEW, but we could not find similar instructions for handling other Kerberos errors, such as KRB_ERR_GENERIC, that may occur during the SMB authentication phase.

Is there a specification or best practice document outlining how the client should handle and recover from each Kerberos error?

Your guidance on this matter would be greatly appreciated.

KristianSmith-MSFT 451 Reputation points Microsoft Employee Moderator

2025-03-25T15:43:50.9266667+00:00

Hi E-8437,

Thanks for reaching out with your Kerberos question. One of our team members will review this and follow up with you soon.

Regards,
Kristian S
Support Escalation Engineer
Microsoft Open Specifications

1 answer

Your answer

KristianSmith-MSFT 451 Reputation points Microsoft Employee Moderator

2025-03-25T15:43:50.9266667+00:00

Hi E-8437,

Thanks for reaching out with your Kerberos question. One of our team members will review this and follow up with you soon.

Regards,
Kristian S
Support Escalation Engineer
Microsoft Open Specifications

Answer 1

KristianSmith-MSFT 451 Microsoft Employee Moderator

Hi E-8437,

The error message KRB_ERR_GENERIC is a broad bucket error as you're likely aware. This is an intentional passive security measure. We do not describe how to handle such an error as there are a vast number of reasons for it to arise. Your best bet is to address the error based on current context (ie: what recent messages were sent, were the messages formatted correctly, etc.).

Thanks again for reaching out with your question.

Regards,
Kristian S
Support Escalation Engineer
Microsoft Open Specifications

E-8437 21 Reputation points

2025-03-26T06:18:19.6733333+00:00
Hi Kristian,

Thank you for your response. I would like further clarification regarding other Kerberos errors that may be encountered during authentication.

In addition to KRB_AP_ERR_SKEW, are there documented guidelines on how an SMB client should handle other recoverable Kerberos errors such as:

KRB_AP_ERR_TKT_EXPIRED

KRB_AP_ERR_REPEAT

KRB_AP_ERR_TKT_NYV

And other similar authentication errors

Is there a specification document that details the appropriate client-side handling and recovery mechanisms for these errors and similar ones?

I would appreciate any documentation or guidance you can provide on this topic.
KristianSmith-MSFT 451 Reputation points Microsoft Employee Moderator

2025-03-26T16:27:17+00:00

Hi E-8437,

I've located some documentation that describes the error flags and associated possible causes in more detail.
https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-10/security/threat-protection/auditing/event-4768#table-2-kerberos-ticket-flags
Remediation steps are not detailed for each error, but this should give you a good starting point to understand what the errors mean.

A good example would be one you've pointed out here: KRB_AP_ERR_TKT_NYV

This error means that the ticket is not yet valid. This information in itself is not a remediation step, because there are multiple possible reasons that this could occur. Your ticket could have been generated with the wrong timestamp or your client and/or server clock could be incorrect or out of sync. A time sync issue may need to be handled outside of Kerberos, depending on the OS and your implementation, therefore the handling of the error is implementation-dependent and cannot be directly specified.

Thanks again for your question. Please let me know if I can provide any clarifications.

Regards,
Kristian Smith
Support Escalation Engineer
Microsoft Open Specifications

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Handling Kerberos Errors in SMB Client Authentication

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