Re: Bug#507633: libgnutls26: GnuTLS does not know VeriSign any more

[Nikos Mavrogiannopoulos]

Simon Josefsson wrote:

>>> gnutls-cli  -p 443 hbci-pintan-rp.s-hbci.de --x509cafile \
>>> /etc/ssl/certs/ca-certificates.crt
>> It seems to me that MD2 is missing from newer gnutls and this is the
>> reason why it fails. libgcrypt has the MD2 enumeration but not the
>> actual implementation and this tricked me into removing the included
>> md2. I will try to revert the old behavior of using an included version
>> of md2.
> 
> I don't think MD2 should be required here: chain verification should not
> need to verify the RSA-MD2 self-signature in the CA cert, because that
> cert is marked as trusted.
> 
> If there were other MD2 signatures involved, verification should
> definitely fail, but that doesn't seem to be the case with this chain.
> 
> It seems this problem is caused by the chain validation algorithm now
> also look at the CA cert, but it didn't before the GNUTLS-SA-2008-3
> patch.

I've added again the GNUTLS-SA-2008-3 patch this time with some checks
to avoid the crashes.

regards,
Nikos

diff --git a/lib/x509/verify.c b/lib/x509/verify.c
index 92ef722..00e2422 100644
--- a/lib/x509/verify.c
+++ b/lib/x509/verify.c
@@ -374,6 +374,24 @@ _gnutls_x509_verify_certificate (const gnutls_x509_crt_t * 
certificate_list,
   int i = 0, ret;
   unsigned int status = 0, output;
 
+  if (clist_size > 1) 
+    {
+      /* Check if the last certificate in the path is self signed.
+       * In that case ignore it (a certificate is trusted only if it
+       * leads to a trusted party by us, not the server's).
+       *
+       * This in addition prevents from verifying self signed certificates
+       * against themselves. This although not bad caused verification
+       * failures on some root self signed certificates that use the MD2
+       * algorithm.
+       */
+      if (gnutls_x509_crt_check_issuer (certificate_list[clist_size - 1],
+                                   certificate_list[clist_size - 1]) > 0)
+        {
+          clist_size--;
+        }
+    }
+
   /* Verify the last certificate in the certificate path
    * against the trusted CA certificate list.
    *