Merge branch 'security-4480-drop-sig0-support' into 'v9.18.28-release'

[9.18] [CVE-2024-1975] Remove support for SIG(0) message verification

See merge request isc-private/bind9!690

CHANGES

@@ -1,3 +1,6 @@
+6402.	[security]	Remove SIG(0) support from named as a countermeasure
+			for CVE-2024-1975. [GL #4480]
+
 6401.	[security]	An excessively large number of rrtypes per owner can
 			slow down database query processing, so a limit has been
 			placed on the number of rrtypes that can be stored per

bin/tests/system/tsiggss/authsock.pl

@@ -33,6 +33,10 @@ if (!defined($path)) {
 	exit(1);
 }
 
+# Enable output autoflush so that it's not lost when the parent sends TERM.
+select STDOUT;
+$| = 1;
+
 unlink($path);
 my $server = IO::Socket::UNIX->new(Local => $path, Type => SOCK_STREAM, Listen => 8) or
     die "unable to create socket $path";
@@ -50,6 +54,7 @@ if ($timeout != 0) {
 }
 
 while (my $client = $server->accept()) {
+	printf("accept()\n");
 	$client->recv(my $buf, 8, 0);
 	my ($version, $req_len) = unpack('N N', $buf);
 

bin/tests/system/tsiggss/tests.sh

@@ -117,7 +117,7 @@ status=$((status + ret))
 
 echo_i "testing external update policy (CNAME) with auth sock ($n)"
 ret=0
-$PERL ./authsock.pl --type=CNAME --path=ns1/auth.sock --pidfile=authsock.pid --timeout=120 >/dev/null 2>&1 &
+$PERL ./authsock.pl --type=CNAME --path=ns1/auth.sock --pidfile=authsock.pid --timeout=120 >authsock.log 2>&1 &
 sleep 1
 test_update $n testcname.example.nil. CNAME "86400 CNAME testdenied.example.nil" "testdenied" || ret=1
 n=$((n + 1))
@@ -131,17 +131,19 @@ n=$((n + 1))
 if [ "$ret" -ne 0 ]; then echo_i "failed"; fi
 status=$((status + ret))
 
-echo_i "testing external policy with SIG(0) key ($n)"
+echo_i "testing external policy with unsupported SIG(0) key ($n)"
 ret=0
-$NSUPDATE -k ns1/Kkey.example.nil.*.private <<END >/dev/null 2>&1 || ret=1
+$NSUPDATE -d -k ns1/Kkey.example.nil.*.private <<END >nsupdate.out${n} 2>&1 || true
+debug
 server 10.53.0.1 ${PORT}
 zone example.nil
 update add fred.example.nil 120 cname foo.bar.
 send
 END
 output=$($DIG $DIGOPTS +short cname fred.example.nil.)
-[ -n "$output" ] || ret=1
-[ $ret -eq 0 ] || echo_i "failed"
+# update must have failed - SIG(0) signer is not supported
+[ -n "$output" ] && ret=1
+grep -F "signer=key.example.nil" authsock.log >/dev/null && ret=1
 n=$((n + 1))
 if [ "$ret" -ne 0 ]; then echo_i "failed"; fi
 status=$((status + ret))

bin/tests/system/upforwd/tests.sh

@@ -229,10 +229,12 @@ fi
 n=$((n + 1))
 
 if test -f keyname; then
-  echo_i "checking update forwarding to with sig0 ($n)"
+  echo_i "checking update forwarding to with sig0 (expected to fail) ($n)"
   ret=0
   keyname=$(cat keyname)
-  $NSUPDATE -k $keyname.private -- - <<EOF
+  # SIG(0) is removed, update is expected to fail.
+  {
+    $NSUPDATE -k $keyname.private -- - <<EOF
 	local 10.53.0.1
 	server 10.53.0.3 ${PORT}
 	zone example2
@@ -240,8 +242,9 @@ if test -f keyname; then
 	update add unsigned.example2. 600 TXT Foo
 	send
 EOF
+  } >nsupdate.out.$n 2>&1 && ret=1
   $DIG -p ${PORT} unsigned.example2 A @10.53.0.1 >dig.out.ns1.test$n || ret=1
-  grep "status: NOERROR" dig.out.ns1.test$n >/dev/null || ret=1
+  grep "status: NOERROR" dig.out.ns1.test$n >/dev/null && ret=1
   if [ $ret != 0 ]; then echo_i "failed"; fi
   status=$((status + ret))
   n=$((n + 1))

doc/arm/general.rst

@@ -391,10 +391,8 @@ Notes
 .. [#rfc1035_2] CLASS ANY queries are not supported. This is considered a
    feature.
 
-.. [#rfc2931] When receiving a query signed with a SIG(0), the server is
-   only able to verify the signature if it has the key in its local
-   authoritative data; it cannot do recursion or validation to
-   retrieve unknown keys.
+.. [#rfc2931] Support for SIG(0) message verification was removed
+   as part of the mitigation of CVE-2024-1975.
 
 .. [#rfc2874] Compliance is with loading and serving of A6 records only.
    A6 records were moved to the experimental category by :rfc:`3363`.

doc/arm/intro-security.inc.rst

@@ -47,7 +47,7 @@ or ports come preconfigured with local (loopback address) security preconfigured
 If ``rndc`` is being invoked from a remote host, further configuration is required.
 The ``nsupdate`` tool uses **Dynamic DNS (DDNS)** features and allows users to dynamically
 change the contents of the zone file(s). ``nsupdate`` access and security may be controlled
-using ``named.conf`` :ref:`statements or using TSIG or SIG(0) cryptographic methods <dynamic_update_security>`.
+using ``named.conf`` :ref:`statements or via the TSIG cryptographic method <dynamic_update_security>`.
 Clearly, if the remote hosts used for either ``rndc`` or DDNS lie within a network entirely
 under the user's control, the security threat may be regarded as non-existent. Any implementation requirements,
 therefore, depend on the site's security policy.

doc/arm/reference.rst

@@ -7450,7 +7450,7 @@ the zone's filename, unless :any:`inline-signing` is enabled.
    updates are allowed. It specifies a set of rules, in which each rule
    either grants or denies permission for one or more names in the zone to
    be updated by one or more identities. Identity is determined by the key
-   that signed the update request, using either TSIG or SIG(0). In most
+   that signed the update request, using TSIG. In most
    cases, :any:`update-policy` rules only apply to key-based identities. There
    is no way to specify update permissions based on the client source address.
 
@@ -7507,7 +7507,7 @@ the zone's filename, unless :any:`inline-signing` is enabled.
    field. Details for each rule type are described below.
 
    The ``identity`` field must be set to a fully qualified domain name. In
-   most cases, this represents the name of the TSIG or SIG(0) key that
+   most cases, this represents the name of the TSIG key that
    must be used to sign the update request. If the specified name is a
    wildcard, it is subject to DNS wildcard expansion, and the rule may
    apply to multiple identities. When a TKEY exchange has been used to

doc/arm/security.inc.rst

@@ -85,7 +85,7 @@ Limiting access to the server by outside parties can help prevent
 spoofing and denial of service (DoS) attacks against the server.
 
 ACLs match clients on the basis of up to three characteristics: 1) The
-client's IP address; 2) the TSIG or SIG(0) key that was used to sign the
+client's IP address; 2) the TSIG key that was used to sign the
 request, if any; and 3) an address prefix encoded in an EDNS
 Client-Subnet option, if any.
 
@@ -126,7 +126,7 @@ and no queries at all from the networks specified in ``bogusnets``.
 
 In addition to network addresses and prefixes, which are matched against
 the source address of the DNS request, ACLs may include ``key``
-elements, which specify the name of a TSIG or SIG(0) key.
+elements, which specify the name of a TSIG key.
 
 When BIND 9 is built with GeoIP support, ACLs can also be used for
 geographic access restrictions. This is done by specifying an ACL

doc/arm/sig0.inc.rst

@@ -12,17 +12,5 @@
 SIG(0)
 ------
 
-BIND partially supports DNSSEC SIG(0) transaction signatures as
-specified in :rfc:`2535` and :rfc:`2931`. SIG(0) uses public/private keys to
-authenticate messages. Access control is performed in the same manner as with
-TSIG keys; privileges can be granted or denied in ACL directives based
-on the key name.
-
-When a SIG(0) signed message is received, it is only verified if
-the key is known and trusted by the server. The server does not attempt
-to recursively fetch or validate the key.
-
-SIG(0) signing of multiple-message TCP streams is not supported.
-
-The only tool shipped with BIND 9 that generates SIG(0) signed messages
-is :iscman:`nsupdate`.
+Support for DNSSEC SIG(0) transaction signatures has been removed.
+This is a countermeasure for CVE-2024-1975.

doc/notes/notes-current.rst

@@ -34,6 +34,11 @@ Security Fixes
   ISC would like to thank Toshifumi Sakaguchi who independently discovered
   and responsibly reported the issue to ISC. :gl:`#4548`
 
+- Validating DNS messages signed using the SIG(0) protocol (:rfc:`2931`) could
+  cause excessive CPU load, leading to a denial-of-service condition.
+  Support for SIG(0) message validation was removed from this version of
+  :iscman:`named`. :cve:`2024-1975` :gl:`#4480`
+
 - Named could trigger an assertion failure when looking up the NS
   records of parent zones as part of looking up DS records.  This
   has been fixed. :gl:`#4661`

lib/dns/message.c

@@ -3292,111 +3292,24 @@ dns_message_dumpsig(dns_message_t *msg, char *txt1) {
 
 isc_result_t
 dns_message_checksig(dns_message_t *msg, dns_view_t *view) {
-	isc_buffer_t b, msgb;
+	isc_buffer_t msgb;
 
 	REQUIRE(DNS_MESSAGE_VALID(msg));
 
-	if (msg->tsigkey == NULL && msg->tsig == NULL && msg->sig0 == NULL) {
+	if (msg->tsigkey == NULL && msg->tsig == NULL) {
 		return (ISC_R_SUCCESS);
 	}
 
 	INSIST(msg->saved.base != NULL);
 	isc_buffer_init(&msgb, msg->saved.base, msg->saved.length);
 	isc_buffer_add(&msgb, msg->saved.length);
-	if (msg->tsigkey != NULL || msg->tsig != NULL) {
 #ifdef SKAN_MSG_DEBUG
-		dns_message_dumpsig(msg, "dns_message_checksig#1");
+	dns_message_dumpsig(msg, "dns_message_checksig#1");
 #endif /* ifdef SKAN_MSG_DEBUG */
-		if (view != NULL) {
-			return (dns_view_checksig(view, &msgb, msg));
-		} else {
-			return (dns_tsig_verify(&msgb, msg, NULL, NULL));
-		}
+	if (view != NULL) {
+		return (dns_view_checksig(view, &msgb, msg));
 	} else {
-		dns_rdata_t rdata = DNS_RDATA_INIT;
-		dns_rdata_sig_t sig;
-		dns_rdataset_t keyset;
-		isc_result_t result;
-
-		result = dns_rdataset_first(msg->sig0);
-		INSIST(result == ISC_R_SUCCESS);
-		dns_rdataset_current(msg->sig0, &rdata);
-
-		/*
-		 * This can occur when the message is a dynamic update, since
-		 * the rdata length checking is relaxed.  This should not
-		 * happen in a well-formed message, since the SIG(0) is only
-		 * looked for in the additional section, and the dynamic update
-		 * meta-records are in the prerequisite and update sections.
-		 */
-		if (rdata.length == 0) {
-			return (ISC_R_UNEXPECTEDEND);
-		}
-
-		result = dns_rdata_tostruct(&rdata, &sig, NULL);
-		if (result != ISC_R_SUCCESS) {
-			return (result);
-		}
-
-		dns_rdataset_init(&keyset);
-		if (view == NULL) {
-			result = DNS_R_KEYUNAUTHORIZED;
-			goto freesig;
-		}
-		result = dns_view_simplefind(view, &sig.signer,
-					     dns_rdatatype_key /* SIG(0) */, 0,
-					     0, false, &keyset, NULL);
-
-		if (result != ISC_R_SUCCESS) {
-			/* XXXBEW Should possibly create a fetch here */
-			result = DNS_R_KEYUNAUTHORIZED;
-			goto freesig;
-		} else if (keyset.trust < dns_trust_secure) {
-			/* XXXBEW Should call a validator here */
-			result = DNS_R_KEYUNAUTHORIZED;
-			goto freesig;
-		}
-		result = dns_rdataset_first(&keyset);
-		INSIST(result == ISC_R_SUCCESS);
-		for (; result == ISC_R_SUCCESS;
-		     result = dns_rdataset_next(&keyset))
-		{
-			dst_key_t *key = NULL;
-
-			dns_rdata_reset(&rdata);
-			dns_rdataset_current(&keyset, &rdata);
-			isc_buffer_init(&b, rdata.data, rdata.length);
-			isc_buffer_add(&b, rdata.length);
-
-			result = dst_key_fromdns(&sig.signer, rdata.rdclass, &b,
-						 view->mctx, &key);
-			if (result != ISC_R_SUCCESS) {
-				continue;
-			}
-			if (dst_key_alg(key) != sig.algorithm ||
-			    dst_key_id(key) != sig.keyid ||
-			    !(dst_key_proto(key) == DNS_KEYPROTO_DNSSEC ||
-			      dst_key_proto(key) == DNS_KEYPROTO_ANY))
-			{
-				dst_key_free(&key);
-				continue;
-			}
-			result = dns_dnssec_verifymessage(&msgb, msg, key);
-			dst_key_free(&key);
-			if (result == ISC_R_SUCCESS) {
-				break;
-			}
-		}
-		if (result == ISC_R_NOMORE) {
-			result = DNS_R_KEYUNAUTHORIZED;
-		}
-
-	freesig:
-		if (dns_rdataset_isassociated(&keyset)) {
-			dns_rdataset_disassociate(&keyset);
-		}
-		dns_rdata_freestruct(&sig);
-		return (result);
+		return (dns_tsig_verify(&msgb, msg, NULL, NULL));
 	}
 }
 

lib/ns/client.c

@@ -2167,6 +2167,13 @@ ns__client_request(isc_nmhandle_t *handle, isc_result_t eresult,
 		ns_client_log(client, DNS_LOGCATEGORY_SECURITY,
 			      NS_LOGMODULE_CLIENT, ISC_LOG_DEBUG(3),
 			      "request is signed by a nonauthoritative key");
+	} else if (result == DNS_R_NOTVERIFIEDYET &&
+		   client->message->sig0 != NULL)
+	{
+		ns_client_log(client, DNS_LOGCATEGORY_SECURITY,
+			      NS_LOGMODULE_CLIENT, ISC_LOG_DEBUG(3),
+			      "request has a SIG(0) signature but its support "
+			      "was removed (CVE-2024-1975)");
 	} else {
 		char tsigrcode[64];
 		isc_buffer_t b;