CVE-2016-2126: auth/kerberos: only allow known checksum types in check_pac_checksum()

aes based checksums can only be checked with the
corresponding aes based keytype.

Otherwise we may trigger an undefined code path
deep in the kerberos libraries, which can leed to
segmentation faults.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12446

Signed-off-by: Stefan Metzmacher <metze@samba.org>

diff --git a/auth/kerberos/kerberos_pac.c b/auth/kerberos/kerberos_pac.c
index 32d9d7fad0edb4ab08dd9dde3d4768a81bf343e6..7b6efdc8db019d54789a75a5415c844bd33d6c82 100644 (file)
--- a/auth/kerberos/kerberos_pac.c
+++ b/auth/kerberos/kerberos_pac.c
@@ -39,6 +39,28 @@ krb5_error_code check_pac_checksum(DATA_BLOB pac_data,
        krb5_boolean checksum_valid = false;
        krb5_data input;
 
+       switch (sig->type) {
+       case CKSUMTYPE_HMAC_MD5:
+               /* ignores the key type */
+               break;
+       case CKSUMTYPE_HMAC_SHA1_96_AES_256:
+               if (KRB5_KEY_TYPE(keyblock) != ENCTYPE_AES256_CTS_HMAC_SHA1_96) {
+                       return EINVAL;
+               }
+               /* ok */
+               break;
+       case CKSUMTYPE_HMAC_SHA1_96_AES_128:
+               if (KRB5_KEY_TYPE(keyblock) != ENCTYPE_AES128_CTS_HMAC_SHA1_96) {
+                       return EINVAL;
+               }
+               /* ok */
+               break;
+       default:
+               DEBUG(2,("check_pac_checksum: Checksum Type %d is not supported\n",
+                       (int)sig->type));
+               return EINVAL;
+       }
+
 #ifdef HAVE_CHECKSUM_IN_KRB5_CHECKSUM /* Heimdal */
        cksum.cksumtype = (krb5_cksumtype)sig->type;
        cksum.checksum.length   = sig->signature.length;