HEIMDAL:kdc: Fix transit path validation CVE-2017-6594

Commit f469fc6 (2010-10-02) inadvertently caused the previous hop realm
to not be added to the transit path of issued tickets.  This may, in
some cases, enable bypass of capath policy in Heimdal versions 1.5
through 7.2.

Note, this may break sites that rely on the bug.  With the bug some
incomplete [capaths] worked, that should not have.  These may now break
authentication in some cross-realm configurations.

(similar to heimdal commit b1e699103f08d6a0ca46a122193c9da65f6cf837)

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12998

Reviewed-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Autobuild-User(master): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(master): Wed Oct 20 10:58:37 UTC 2021 on sn-devel-184

diff --git a/source4/heimdal/kdc/krb5tgs.c b/source4/heimdal/kdc/krb5tgs.c
index 2de3b09919975f60a1d78982747614150d8bfd25..7e9379db64a38e735e85d42ce4752ff04cd5bacf 100644 (file)
--- a/source4/heimdal/kdc/krb5tgs.c
+++ b/source4/heimdal/kdc/krb5tgs.c
@@ -409,8 +409,12 @@ fix_transited_encoding(krb5_context context,
                  "Decoding transited encoding");
        return ret;
     }
+
+    /*
+     * If the realm of the presented tgt is neither the client nor the server
+     * realm, it is a transit realm and must be added to transited set.
+     */
     if(strcmp(client_realm, tgt_realm) && strcmp(server_realm, tgt_realm)) {
-       /* not us, so add the previous realm to transited set */
        if (num_realms + 1 > UINT_MAX/sizeof(*realms)) {
            ret = ERANGE;
            goto free_realms;
@@ -492,6 +496,7 @@ tgs_make_reply(krb5_context context,
               const char *server_name,
               hdb_entry_ex *client,
               krb5_principal client_principal,
+               const char *tgt_realm,
               hdb_entry_ex *krbtgt,
               krb5_pac mspac,
               uint16_t rodc_id,
@@ -553,7 +558,7 @@ tgs_make_reply(krb5_context context,
                                 &tgt->transited, &et,
                                 krb5_principal_get_realm(context, client_principal),
                                 krb5_principal_get_realm(context, server->entry.principal),
-                                krb5_principal_get_realm(context, krbtgt->entry.principal));
+                                tgt_realm);
     if(ret)
        goto out;
 
@@ -1292,13 +1297,14 @@ tgs_build_reply(krb5_context context,
     HDB *clientdb, *s4u2self_impersonated_clientdb;
     krb5_realm ref_realm = NULL;
     EncTicketPart *tgt = &ticket->ticket;
+    const char *tgt_realm = /* Realm of TGT issuer */
+        krb5_principal_get_realm(context, krbtgt->entry.principal);
     const EncryptionKey *ekey;
     krb5_keyblock sessionkey;
     krb5_kvno kvno;
     krb5_pac mspac = NULL;
     uint16_t rodc_id;
     krb5_boolean add_ticket_sig = FALSE;
-
     hdb_entry_ex *krbtgt_out = NULL;
 
     METHOD_DATA enc_pa_data;
@@ -2036,6 +2042,7 @@ server_lookup:
                         spn,
                         client,
                         cp,
+                        tgt_realm,
                         krbtgt_out,
                         mspac,
                         rodc_id,