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.
2016-08-10 23:31:14 +00:00
parent d5dd5aab19
commit b1e699103f
4 changed files with 45 additions and 2 deletions
--- a/14
+++ b/14
@@ -1,3 +1,17 @@
+Release Notes - Heimdal - Version Heimdal 7.3
+
+ Security
+
+ - Fix transit path validation.  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.
+   (CVE-2017-6594)
+
 Release Notes - Heimdal - Version Heimdal 7.2

 Bug fixes
--- a/kdc/krb5tgs.c
+++ b/kdc/krb5tgs.c
@@ -655,8 +655,12 @@ 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;
@@ -737,6 +741,7 @@ 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_enctype krbtgt_etype,
 	       krb5_principals spp,
@@ -798,7 +803,7 @@ 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;

@@ -1519,6 +1524,8 @@ tgs_build_reply(krb5_context context,
    krb5_keyblock sessionkey;
    krb5_kvno kvno;
    krb5_data rspac;
+    const char *tgt_realm = /* Realm of TGT issuer */
+        krb5_principal_get_realm(context, krbtgt->entry.principal);
    const char *our_realm = /* Realm of this KDC */
        krb5_principal_get_comp_string(context, krbtgt->entry.principal, 1);
    char **capath = NULL;
@@ -2324,6 +2331,7 @@ server_lookup:
 			 spn,
 			 client,
 			 cp,
+                         tgt_realm,
 			 krbtgt_out,
 			 tkey_sign->key.keytype,
 			 spp,
--- a/tests/kdc/check-kdc.in
+++ b/tests/kdc/check-kdc.in
@@ -53,6 +53,7 @@ R4=TEST4.H5L.SE
 R5=SOME-REALM5.FR
 R6=SOME-REALM6.US
 R7=SOME-REALM7.UK
+R8=SOME-REALM8.UK

 H1=H1.$R
 H2=H2.$R
@@ -148,6 +149,12 @@ ${kadmin} \
    --realm-max-renewable-life=1month \
    ${R7} || exit 1

+${kadmin} \
+    init \
+    --realm-max-ticket-life=1day \
+    --realm-max-renewable-life=1month \
+    ${R8} || exit 1
+
 ${kadmin} \
    init \
    --realm-max-ticket-life=1day \
@@ -191,6 +198,7 @@ ${kadmin} add -p foo --use-defaults foo@${R4} || exit 1
 ${kadmin5} add -p foo --use-defaults foo@${R5} || exit 1
 ${kadmin} add -p foo --use-defaults foo@${R6} || exit 1
 ${kadmin} add -p foo --use-defaults foo@${R7} || exit 1
+${kadmin} add -p foo --use-defaults foo@${R8} || exit 1
 ${kadmin} add -p foo --use-defaults foo@${H1} || exit 1
 ${kadmin} add -p foo --use-defaults foo/host.${h1}@${H1} || exit 1
 ${kadmin} add -p foo --use-defaults foo@${H2} || exit 1
@@ -249,6 +257,9 @@ ${kadmin} add -p cross2 --use-defaults krbtgt/${R5}@${R6} || exit 1
 ${kadmin} add -p cross1 --use-defaults krbtgt/${R7}@${R6} || exit 1
 ${kadmin} add -p cross2 --use-defaults krbtgt/${R6}@${R7} || exit 1

+${kadmin} add -p cross1 --use-defaults krbtgt/${R8}@${R6} || exit 1
+${kadmin} add -p cross2 --use-defaults krbtgt/${R6}@${R8} || exit 1
+
 ${kadmin} add -p cross1 --use-defaults krbtgt/${H1}@${R} || exit 1
 ${kadmin} add -p cross2 --use-defaults krbtgt/${R}@${H1} || exit 1

@@ -284,6 +295,7 @@ ${kadmin} check ${R4} || exit 1
 ${kadmin5} check ${R5} || exit 1
 ${kadmin} check ${R6} || exit 1
 ${kadmin} check ${R7} || exit 1
+${kadmin} check ${R8} || exit 1
 ${kadmin} check ${H1} || exit 1
 ${kadmin} check ${H2} || exit 1
 ${kadmin} check ${H3} || exit 1
@@ -388,6 +400,8 @@ echo "Getting x-realm tickets with capaths for $R -> $R6"
 ${kgetcred} foo@${R6} || { ec=1 ; eval "${testfailed}"; }
 echo "Getting x-realm tickets with capaths for $R -> $R7"
 ${kgetcred} foo@${R7} || { ec=1 ; eval "${testfailed}"; }
+echo "Should not get x-realm tickets with capaths for $R -> $R8"
+${kgetcred} foo@${R8} && { ec=1 ; eval "${testfailed}"; }
 ${kdestroy}

 echo "Testing capaths logic (reverse order)"
@@ -418,10 +432,13 @@ ${kinit} --password-file=${objdir}/foopassword \

 echo "Getting x-realm tickets with hierarchical referrals for $H3 -> $H1"
 ${kgetcred} --hostbased --canonicalize foo host.${h1} || { ec=1 ; eval "${testfailed}"; }
+fgrep "cross-realm ${H3} -> ${H1} via [${H2}, ${R}]" messages.log > /dev/null || { ec=1 ; eval "${testfailed}"; }
 echo "Getting x-realm tickets with hierarchical referrals for $H3 -> $R"
 ${kgetcred} --hostbased --canonicalize foo host.${r} || { ec=1 ; eval "${testfailed}"; }
+fgrep "cross-realm ${H3} -> ${R} via [${H2}]" messages.log > /dev/null || { ec=1 ; eval "${testfailed}"; }
 echo "Getting x-realm tickets with hierarchical referrals for $H3 -> $H2"
 ${kgetcred} --hostbased --canonicalize foo host.${h2} || { ec=1 ; eval "${testfailed}"; }
+fgrep "cross-realm ${H3} -> ${H2}" messages.log > /dev/null || { ec=1 ; eval "${testfailed}"; }
 ${kdestroy}

 echo "Testing multi-hop [capaths] referral logic"
--- a/tests/kdc/krb5.conf.in
+++ b/tests/kdc/krb5.conf.in
@@ -40,6 +40,9 @@
 	SOME-REALM7.UK = {
 		kdc = localhost:@port@
 	}
+	SOME-REALM8.UK = {
+		kdc = localhost:@port@
+	}
 	TEST-HTTP.H5L.SE = {
 		kdc = http/localhost:@port@
 	}
@@ -147,6 +150,7 @@
 		SOME-REALM6.US = SOME-REALM5.FR
 		SOME-REALM7.UK = SOME-REALM6.US
 		SOME-REALM7.UK = SOME-REALM5.FR
+		SOME-REALM8.UK = SOME-REALM6.US
 	}
        H4.H2.TEST.H5L.SE = {
                H1.TEST.H5L.SE = H3.H2.TEST.H5L.SE