From ec67f14dc90e17acf08708e53a2166e0554b25ca Mon Sep 17 00:00:00 2001 From: Petr Mensik Date: Tue, 16 Jul 2024 19:49:09 +0200 Subject: [PATCH] Resolve CVE-2024-1975 6404. [security] Remove SIG(0) support from named as a countermeasure for CVE-2024-1975. [GL #4480] Resolves: CVE-2024-1975 --- bin/tests/system/tsiggss/authsock.pl | 5 ++ bin/tests/system/tsiggss/tests.sh | 12 ++-- bin/tests/system/upforwd/tests.sh | 21 +++--- doc/arm/general.rst | 6 +- doc/arm/reference.rst | 4 +- doc/arm/security.rst | 4 +- lib/dns/message.c | 99 ++-------------------------- lib/ns/client.c | 7 ++ 8 files changed, 43 insertions(+), 115 deletions(-) diff --git a/bin/tests/system/tsiggss/authsock.pl b/bin/tests/system/tsiggss/authsock.pl index d629c65..b3888fb 100644 --- a/bin/tests/system/tsiggss/authsock.pl +++ b/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 $path"; @@ -55,6 +59,7 @@ if ($timeout != 0) { } while (my $client = $server->accept()) { + printf("accept()\n"); $client->recv(my $buf, 8, 0); my ($version, $req_len) = unpack('N N', $buf); diff --git a/bin/tests/system/tsiggss/tests.sh b/bin/tests/system/tsiggss/tests.sh index a665703..34b8c89 100644 --- a/bin/tests/system/tsiggss/tests.sh +++ b/bin/tests/system/tsiggss/tests.sh @@ -116,7 +116,7 @@ status=$((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)) @@ -130,17 +130,19 @@ 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 </dev/null 2>&1 || ret=1 +$NSUPDATE -d -k ns1/Kkey.example.nil.*.private <nsupdate.out${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)) diff --git a/bin/tests/system/upforwd/tests.sh b/bin/tests/system/upforwd/tests.sh index 063e28d..0947166 100644 --- a/bin/tests/system/upforwd/tests.sh +++ b/bin/tests/system/upforwd/tests.sh @@ -262,19 +262,22 @@ if $FEATURETEST --enable-dnstap; then fi if test -f keyname; then - echo_i "checking update forwarding to with sig0 ($n)" + echo_i "checking update forwarding to with sig0 (expected to fail) ($n)" ret=0 keyname=$(cat keyname) - $NSUPDATE -k $keyname.private -- - <nsupdate.out.$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 [ $ret != 0 ]; then echo_i "failed"; fi status=$(expr $status + $ret) n=$(expr $n + 1) diff --git a/doc/arm/general.rst b/doc/arm/general.rst index d7b7c20..59f9e6b 100644 --- a/doc/arm/general.rst +++ b/doc/arm/general.rst @@ -367,10 +367,8 @@ 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`. diff --git a/doc/arm/reference.rst b/doc/arm/reference.rst index ecc84d4..f982e0a 100644 --- a/doc/arm/reference.rst +++ b/doc/arm/reference.rst @@ -5900,7 +5900,7 @@ The ``update-policy`` clause allows more fine-grained control over which 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 either TSIG. In most cases, ``update-policy`` rules only apply to key-based identities. There is no way to specify update permissions based on the client source address. @@ -5957,7 +5957,7 @@ field), and the type of the record to be updated matches the ``types`` 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 diff --git a/doc/arm/security.rst b/doc/arm/security.rst index 817ebd0..92b1668 100644 --- a/doc/arm/security.rst +++ b/doc/arm/security.rst @@ -83,7 +83,7 @@ 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. @@ -124,7 +124,7 @@ 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 diff --git a/lib/dns/message.c b/lib/dns/message.c index 22aa552..12331ab 100644 --- a/lib/dns/message.c +++ b/lib/dns/message.c @@ -3301,111 +3301,24 @@ 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)); } } diff --git a/lib/ns/client.c b/lib/ns/client.c index d4ce000..2679a5e 100644 --- a/lib/ns/client.c +++ b/lib/ns/client.c @@ -2041,6 +2041,13 @@ 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; -- 2.51.1