possible ways to exploit CVE-2012-1663

CVE-2013-1663 is a possible remote DOS attack issue. This issue has
been fixed in >=GNUTLS-3.0.14. I hacked on it for hours and figure out
a few prerequisites could make it vulnerable:

=============================
REQUIRED:

 - prior to GNUTLS 3.0.14
 - crafted certificate

=============================
Attacking SCENES

 - a client import a crafted cert file for sending req to server( CA?)

 - a "server" import a crafted cert file for sending req to other
   server( CA?)

---> With high frequency uses above manipulations

Stand on the client side, the attacker should try to construct a
crafted certificate for triggering the below function fails:

ret = gnutls_pubkey_import_x509(pcert->pubkey, crt, 0);
  if (ret < 0)
    {
      gnutls_pubkey_deinit(pcert->pubkey);
      /* pcert->pubkey should be NULL now */
      ret = gnutls_assert_val(ret);
      goto cleanup;
    }

I made up two crafted cert files( client.pem, client2.pem) seems would
trigger the double free issue in client's side.

Warning: Don't try it on your host machine because it would cost too
much memory then makes your machine very slow. I highly recommend you guys use vm for testing.

shawn@sl13:~/gnutls_compile_uses/CVE-2012-1663$ ./ex-serv-x509
processing server set to null?
Server ready. Listening to port '5556'.

shawn@sl13:~/gnutls_compile_uses/CVE-2012-1663$ ./attack.sh
................
.................
...................

Another terminal: killall client

Test platform: Slackware 13.37 + GNUTLS-3.0.13