MITKRB5-SA-2010-001 CVE-2010-0283 KDC denial of service

Code introduced in krb5-1.7 can cause an assertion failure if a
KDC-REQ is internally inconsistent, specifically if the ASN.1 tag
doesn't match the msg_type field.  Thanks to Emmanuel Bouillon (NATO
C3 Agency) for discovering and reporting this vulnerability.

ticket: 6662
tags: pullup
target_version: 1.8

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@23724 dc483132-0cff-0310-8789-dd5450dbe970

src/kdc/do_as_req.c

@@ -139,6 +139,11 @@ process_as_req(krb5_kdc_req *request, krb5_data *req_pkt,
     session_key.contents = 0;
     enc_tkt_reply.authorization_data = NULL;
 
+    if (request->msg_type != KRB5_AS_REQ) {
+        status = "msg_type mismatch";
+        errcode = KRB5_BADMSGTYPE;
+        goto errout;
+    }
     errcode = kdc_make_rstate(&state);
     if (errcode != 0) {
         status = "constructing state";

src/kdc/do_tgs_req.c

@@ -143,6 +143,8 @@ process_tgs_req(krb5_data *pkt, const krb5_fulladdr *from,
     retval = decode_krb5_tgs_req(pkt, &request);
     if (retval)
         return retval;
+    if (request->msg_type != KRB5_TGS_REQ)
+        return KRB5_BADMSGTYPE;
 
     /*
      * setup_server_realm() sets up the global realm-specific data pointer.

src/kdc/fast_util.c

@@ -384,7 +384,7 @@ kdc_fast_handle_error(krb5_context context,
     krb5_data *encoded_e_data = NULL;
 
     memset(outer_pa, 0, sizeof(outer_pa));
-    if (!state->armor_key)
+    if (!state || !state->armor_key)
         return 0;
     fx_error = *err;
     fx_error.e_data.data = NULL;