X.509 certificate verification in GNU TLS Library

[Simon Josefsson]

Guido Trentalancia <guido at trentalancia.com> writes:

> Hello,
>
> I have tested the current GNU TLS Library against the issue reported at
> http://article.gmane.org/gmane.comp.encryption.gpg.gnutls.devel/3517 and
> I believe the function _gnutls_x509_verify_certificate() in
> lib/x509/verify.c needs to be modified according to the attached patch
> in order for the certificate verification to work properly.
>
> In fact, at the moment (version 2.8.4 and at least since the problem was
> originally reported against branch 2.4.x as GNUTLS-SA-2009-3), the
> certificate verification function returns the status after each check,
> which implies that not all checks in _gnutls_x509_verify_certificate()
> are necessarily performed. I believe the correct behaviour is that all
> checks need to be performed (and stored in the variable "status" using
> logical OR) and that the result in the variable "status" need to be
> returned only then.
>
> After the attached patch is applied, the function returns only at the
> end, after all the checks have been performed (and the result contained
> in the variable "status" is the logical OR of the results of each check
> performed).
>
> What I get is that only using this patch, the behaviour is consistent
> with the expected results, as they have been outlined in the article
> mentioned above.
>
> Could somebody please double-check and eventually confirm ? Thanks.

Some test vectors would help to reinforce and explain your point, do you
have a test X.509 chain that validates incorrectly that you could post?

/Simon