gensec returns the wrong error to kerberos errors like Ticket Expired and clock skew issues

Richard Sharpe realrichardsharpe at
Wed Nov 4 19:14:50 UTC 2015

On Wed, Nov 4, 2015 at 10:22 AM, Jeremy Allison <jra at> wrote:
> On Wed, Nov 04, 2015 at 10:00:48AM -0800, Richard Sharpe wrote:
>> Hi folks,
>> A capture I have indicates that when a Windows server gets a
>> KRB5KRB_AP_ERR_TKT_EXPIRED error it returns
>> STATUS_MORE_PROCESSING_REQUIRED along with an SPNEGO negTokenTarg with
>> the Kerberos error blob in it.
>> Samba, and it looks like gensec, folds that down to LOGON_FAILED,
>> which makes it very hard for admins to figure out what the real error
>> is.
>> Is there a bugzilla on this?
>> If I get a chance I will try to provide a fix.
> I think that is intentional in order to prevent
> username guessing attacks.

That doesn't even pass the smell test. The KDC is responsible for
preventing password guessing games.

In this case the KDC issued a valid ticket, but because of a large
amount of clock skew between the server and the issuer the ticket was
regarded as expired.

Windows pops up a message telling the user that there is too much
clock skew in this case.

With the Samba response the user is simply prompted for his creds again.

> Does the real error get logged inside Samba
> somewhere ?

I am getting the QA guy to redo the tests and get me the Samba logs.

Richard Sharpe

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