tls: drop support for URI alternative names

Previously, Node.js incorrectly accepted uniformResourceIdentifier (URI)
subject alternative names in checkServerIdentity regardless of the
application protocol. This was incorrect even in the most common cases.
For example, RFC 2818 specifies (and RFC 6125 confirms) that HTTP over
TLS only uses dNSName and iPAddress subject alternative names, but not
uniformResourceIdentifier subject alternative names.

Additionally, name constrained certificate authorities might not be
constrained to specific URIs, allowing them to issue certificates for
URIs that specify hosts that they would not be allowed to issue dNSName
certificates for.

Even for application protocols that make use of URI subject alternative
names (such as SIP, see RFC 5922), Node.js did not implement the
required checks correctly, for example, because checkServerIdentity
ignores the URI scheme.

As a side effect, this also fixes an edge case. When a hostname is not
an IP address and no dNSName subject alternative name exists, the
subject's Common Name should be considered even when an iPAddress
subject alternative name exists.

It remains possible for users to pass a custom checkServerIdentity
function to the TLS implementation in order to implement custom identity
verification logic.

This addresses CVE-2021-44531.

Co-authored-by: Akshay K <iit.akshay@gmail.com>
CVE-ID: CVE-2021-44531
Backport-PR-URL: nodejs-private/node-private#304
PR-URL: nodejs-private/node-private#300
Reviewed-By: Michael Dawson <midawson@redhat.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

Author: 2 people

doc/api/tls.md

@@ -1453,6 +1453,11 @@ decrease overall server throughput.
 
 <!-- YAML
 added: v0.8.4
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs-private/node-private/pull/300
+    description: Support for `uniformResourceIdentifier` subject alternative
+                 names has been disabled in response to CVE-2021-44531.
 -->
 
 * `hostname` {string} The host name or IP address to verify the certificate
@@ -1473,6 +1478,12 @@ the checks done with additional verification.
 This function is only called if the certificate passed all other checks, such as
 being issued by trusted CA (`options.ca`).
 
+Earlier versions of Node.js incorrectly accepted certificates for a given
+`hostname` if a matching `uniformResourceIdentifier` subject alternative name
+was present (see [CVE-2021-44531][]). Applications that wish to accept
+`uniformResourceIdentifier` subject alternative names can use a custom
+`options.checkServerIdentity` function that implements the desired behavior.
+
 ## `tls.connect(options[, callback])`
 
 <!-- YAML
@@ -2134,6 +2145,7 @@ added: v11.4.0
   `'TLSv1.3'`. If multiple of the options are provided, the lowest minimum is
   used.
 
+[CVE-2021-44531]: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-44531
 [Chrome's 'modern cryptography' setting]: https://www.chromium.org/Home/chromium-security/education/tls#TOC-Cipher-Suites
 [DHE]: https://en.wikipedia.org/wiki/Diffie%E2%80%93Hellman_key_exchange
 [ECDHE]: https://en.wikipedia.org/wiki/Elliptic_curve_Diffie%E2%80%93Hellman

lib/tls.js

@@ -60,7 +60,6 @@ const net = require('net');
 const { getOptionValue } = require('internal/options');
 const { getRootCertificates, getSSLCiphers } = internalBinding('crypto');
 const { Buffer } = require('buffer');
-const { URL } = require('internal/url');
 const { canonicalizeIP } = internalBinding('cares_wrap');
 const _tls_common = require('_tls_common');
 const _tls_wrap = require('_tls_wrap');
@@ -275,7 +274,6 @@ exports.checkServerIdentity = function checkServerIdentity(hostname, cert) {
   const subject = cert.subject;
   const altNames = cert.subjectaltname;
   const dnsNames = [];
-  const uriNames = [];
   const ips = [];
 
   hostname = '' + hostname;
@@ -287,11 +285,6 @@ exports.checkServerIdentity = function checkServerIdentity(hostname, cert) {
     ArrayPrototypeForEach(splitAltNames, (name) => {
       if (StringPrototypeStartsWith(name, 'DNS:')) {
         ArrayPrototypePush(dnsNames, StringPrototypeSlice(name, 4));
-      } else if (StringPrototypeStartsWith(name, 'URI:')) {
-        const uri = new URL(StringPrototypeSlice(name, 4));
-
-        // TODO(bnoordhuis) Also use scheme.
-        ArrayPrototypePush(uriNames, uri.hostname);
       } else if (StringPrototypeStartsWith(name, 'IP Address:')) {
         ArrayPrototypePush(ips, canonicalizeIP(StringPrototypeSlice(name, 11)));
       }
@@ -301,25 +294,19 @@ exports.checkServerIdentity = function checkServerIdentity(hostname, cert) {
   let valid = false;
   let reason = 'Unknown reason';
 
-  const hasAltNames =
-    dnsNames.length > 0 || ips.length > 0 || uriNames.length > 0;
-
   hostname = unfqdn(hostname);  // Remove trailing dot for error messages.
 
   if (net.isIP(hostname)) {
     valid = ArrayPrototypeIncludes(ips, canonicalizeIP(hostname));
     if (!valid)
       reason = `IP: ${hostname} is not in the cert's list: ` +
                ArrayPrototypeJoin(ips, ', ');
-    // TODO(bnoordhuis) Also check URI SANs that are IP addresses.
-  } else if (hasAltNames || subject) {
+  } else if (dnsNames.length > 0 || subject?.CN) {
     const hostParts = splitHost(hostname);
     const wildcard = (pattern) => check(hostParts, pattern, true);
 
-    if (hasAltNames) {
-      const noWildcard = (pattern) => check(hostParts, pattern, false);
-      valid = ArrayPrototypeSome(dnsNames, wildcard) ||
-              ArrayPrototypeSome(uriNames, noWildcard);
+    if (dnsNames.length > 0) {
+      valid = ArrayPrototypeSome(dnsNames, wildcard);
       if (!valid)
         reason =
           `Host: ${hostname}. is not in the cert's altnames: ${altNames}`;
@@ -336,7 +323,7 @@ exports.checkServerIdentity = function checkServerIdentity(hostname, cert) {
         reason = `Host: ${hostname}. is not cert's CN: ${cn}`;
     }
   } else {
-    reason = 'Cert is empty';
+    reason = 'Cert does not contain a DNS name';
   }
 
   if (!valid) {

test/fixtures/keys/Makefile

@@ -87,6 +87,8 @@ all: \
   ec_secp256k1_public.pem \
   incorrect_san_correct_subject-cert.pem \
   incorrect_san_correct_subject-key.pem \
+  irrelevant_san_correct_subject-cert.pem \
+  irrelevant_san_correct_subject-key.pem \
 
 #
 # Create Certificate Authority: ca1
@@ -795,6 +797,18 @@ incorrect_san_correct_subject-cert.pem: incorrect_san_correct_subject-key.pem
 incorrect_san_correct_subject-key.pem:
 	openssl ecparam -name prime256v1 -genkey -noout -out incorrect_san_correct_subject-key.pem
 
+irrelevant_san_correct_subject-cert.pem: irrelevant_san_correct_subject-key.pem
+	openssl req -x509 \
+	            -key irrelevant_san_correct_subject-key.pem \
+	            -out irrelevant_san_correct_subject-cert.pem \
+	            -sha256 \
+	            -days 3650 \
+	            -subj "/CN=good.example.com" \
+	            -addext "subjectAltName = IP:1.2.3.4"
+
+irrelevant_san_correct_subject-key.pem:
+	openssl ecparam -name prime256v1 -genkey -noout -out irrelevant_san_correct_subject-key.pem
+
 clean:
 	rm -f *.pfx *.pem *.srl ca2-database.txt ca2-serial fake-startcom-root-serial *.print *.old fake-startcom-root-issued-certs/*.pem
 	@> fake-startcom-root-database.txt

test/fixtures/keys/irrelevant_san_correct_subject-cert.pem

@@ -0,0 +1,11 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----

test/fixtures/keys/irrelevant_san_correct_subject-key.pem

@@ -0,0 +1,5 @@
+-----BEGIN EC PRIVATE KEY-----
+MHcCAQEEIDsijdVlHMNTvJ4eqeUbpjMMnl72+HLtEIEcbauckCP6oAoGCCqGSM49
+AwEHoUQDQgAExCqCXw7ykOnQ/sr3OA2nh9GZRvFbhiVFYuoiG7oGN3Sh3Zl1CLsM
+FEnIM7S3OlvBX7208X0xdqvdGQSZa/ypbw==
+-----END EC PRIVATE KEY-----

test/parallel/test-tls-check-server-identity.js

@@ -134,7 +134,7 @@ const tests = [
   {
     host: 'a.com',
     cert: { },
-    error: 'Cert is empty'
+    error: 'Cert does not contain a DNS name'
   },
 
   // Empty Subject w/DNS name
@@ -148,7 +148,8 @@ const tests = [
   {
     host: 'a.b.a.com', cert: {
       subjectaltname: 'URI:http://a.b.a.com/',
-    }
+    },
+    error: 'Cert does not contain a DNS name'
   },
 
   // Multiple CN fields
@@ -265,24 +266,23 @@ const tests = [
     host: 'a.b.a.com', cert: {
       subjectaltname: 'URI:http://a.b.a.com/',
       subject: {}
-    }
+    },
+    error: 'Cert does not contain a DNS name'
   },
   {
     host: 'a.b.a.com', cert: {
       subjectaltname: 'URI:http://*.b.a.com/',
       subject: {}
     },
-    error: 'Host: a.b.a.com. is not in the cert\'s altnames: ' +
-           'URI:http://*.b.a.com/'
+    error: 'Cert does not contain a DNS name'
   },
   // IP addresses
   {
     host: 'a.b.a.com', cert: {
       subjectaltname: 'IP Address:127.0.0.1',
       subject: {}
     },
-    error: 'Host: a.b.a.com. is not in the cert\'s altnames: ' +
-           'IP Address:127.0.0.1'
+    error: 'Cert does not contain a DNS name'
   },
   {
     host: '127.0.0.1', cert: {

test/parallel/test-x509-escaping.js

@@ -20,10 +20,6 @@ const { hasOpenSSL3 } = common;
   const numLeaves = 5;
 
   for (let i = 0; i < numLeaves; i++) {
-    // TODO(tniessen): this test case requires proper handling of URI SANs,
-    // which node currently does not implement.
-    if (i === 3) continue;
-
     const name = `x509-escaping/google/leaf${i}.pem`;
     const leafPEM = fixtures.readSync(name, 'utf8');
 
@@ -336,3 +332,30 @@ const { hasOpenSSL3 } = common;
     }));
   })).unref();
 }
+
+// The subject MUST NOT be ignored if no dNSName subject alternative name
+// exists, even if other subject alternative names exist.
+{
+  const key = fixtures.readKey('irrelevant_san_correct_subject-key.pem');
+  const cert = fixtures.readKey('irrelevant_san_correct_subject-cert.pem');
+
+  // The hostname is the CN, but there is no dNSName SAN entry.
+  const servername = 'good.example.com';
+  const certX509 = new X509Certificate(cert);
+  assert.strictEqual(certX509.subject, `CN=${servername}`);
+  assert.strictEqual(certX509.subjectAltName, 'IP Address:1.2.3.4');
+
+  // Connect to a server that uses the self-signed certificate.
+  const server = tls.createServer({ key, cert }, common.mustCall((socket) => {
+    socket.destroy();
+    server.close();
+  })).listen(common.mustCall(() => {
+    const { port } = server.address();
+    tls.connect(port, {
+      ca: cert,
+      servername,
+    }, common.mustCall(() => {
+      // Do nothing, the server will close the connection.
+    }));
+  }));
+}