krb5 commit [krb5-1.10]: PKINIT (draft9) null ptr deref [CVE-2012-1016]

[Tom Yu]

https://github.com/krb5/krb5/commit/db64ca25d661a47b996b4e2645998b5d7f0eb52c
commit db64ca25d661a47b996b4e2645998b5d7f0eb52c
Author: Nalin Dahyabhai <nalin at redhat.com>
Date:   Thu Dec 13 14:26:07 2012 -0500

    PKINIT (draft9) null ptr deref [CVE-2012-1016]
    
    Don't check for an agility KDF identifier in the non-draft9 reply
    structure when we're building a draft9 reply, because it'll be NULL.
    
    The KDC plugin for PKINIT can dereference a null pointer when handling
    a draft9 request, leading to a crash of the KDC process.  An attacker
    would need to have a valid PKINIT certificate, or an unauthenticated
    attacker could execute the attack if anonymous PKINIT is enabled.
    
    CVSSv2 vector: AV:N/AC:M/Au:N/C:N/I:N/A:P/E:P/RL:O/RC:C
    
    [tlyu at mit.edu: reformat comment and edit log message]
    
    (back ported from commit cd5ff932c9d1439c961b0cf9ccff979356686aff)
    
    ticket: 7527 (new)
    version_fixed: 1.10.4
    status: resolved

 src/plugins/preauth/pkinit/pkinit_srv.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/plugins/preauth/pkinit/pkinit_srv.c b/src/plugins/preauth/pkinit/pkinit_srv.c
index 3322310..c271bf9 100644
--- a/src/plugins/preauth/pkinit/pkinit_srv.c
+++ b/src/plugins/preauth/pkinit/pkinit_srv.c
@@ -1016,9 +1016,10 @@ pkinit_server_return_padata(krb5_context context,
          rep9->choice == choice_pa_pk_as_rep_draft9_dhSignedData) ||
         (rep != NULL && rep->choice == choice_pa_pk_as_rep_dhInfo)) {
 
-        /* If mutually supported KDFs were found, use the alg agility KDF */
-        if (rep->u.dh_Info.kdfID) {
-            secret.data = server_key;
+        /* If we're not doing draft 9, and mutually supported KDFs were found,
+         * use the algorithm agility KDF. */
+        if (rep != NULL && rep->u.dh_Info.kdfID) {
+            secret.data = (char *)server_key;
             secret.length = server_key_len;
 
             retval = pkinit_alg_agility_kdf(context, &secret,