crypto,tls: implement safe x509 GeneralName format

This change introduces JSON-compatible escaping rules for strings that
include X.509 GeneralName components (see RFC 5280). This non-standard
format avoids ambiguities and prevents injection attacks that could
previously lead to X.509 certificates being accepted even though they
were not valid for the target hostname.

These changes affect the format of subject alternative names and the
format of authority information access. The checkServerIdentity function
has been modified to safely handle the new format, eliminating the
possibility of injecting subject alternative names into the verification
logic.

Because each subject alternative name is only encoded as a JSON string
literal if necessary for security purposes, this change will only be
visible in rare cases.

This addresses CVE-2021-44532.

Co-authored-by: Akshay K <iit.akshay@gmail.com>
CVE-ID: CVE-2021-44532
Backport-PR-URL: nodejs-private/node-private#305
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/errors.md

@@ -1975,6 +1975,14 @@ An unspecified or non-specific system error has occurred within the Node.js
 process. The error object will have an `err.info` object property with
 additional details.
 
+<a id="ERR_TLS_CERT_ALTNAME_FORMAT"></a>
+### `ERR_TLS_CERT_ALTNAME_FORMAT`
+
+This error is thrown by `checkServerIdentity` if a user-supplied
+`subjectaltname` property violates encoding rules. Certificate objects produced
+by Node.js itself always comply with encoding rules and will never cause
+this error.
+
 <a id="ERR_TLS_CERT_ALTNAME_INVALID"></a>
 ### `ERR_TLS_CERT_ALTNAME_INVALID`
 

lib/_tls_common.js

@@ -23,6 +23,7 @@
 
 const {
   ArrayIsArray,
+  JSONParse,
   ObjectCreate,
 } = primordials;
 
@@ -323,6 +324,14 @@ exports.translatePeerCertificate = function translatePeerCertificate(c) {
 
     // XXX: More key validation?
     info.replace(/([^\n:]*):([^\n]*)(?:\n|$)/g, (all, key, val) => {
+      if (val.charCodeAt(0) === 0x22) {
+        // The translatePeerCertificate function is only
+        // used on internally created legacy certificate
+        // objects, and any value that contains a quote
+        // will always be a valid JSON string literal,
+        // so this should never throw.
+        val = JSONParse(val);
+      }
       if (key in c.infoAccess)
         c.infoAccess[key].push(val);
       else

lib/internal/errors.js

@@ -1410,6 +1410,8 @@ E('ERR_STREAM_WRAP', 'Stream has StringDecoder set or is in objectMode', Error);
 E('ERR_STREAM_WRITE_AFTER_END', 'write after end', Error);
 E('ERR_SYNTHETIC', 'JavaScript Callstack', Error);
 E('ERR_SYSTEM_ERROR', 'A system error occurred', SystemError);
+E('ERR_TLS_CERT_ALTNAME_FORMAT', 'Invalid subject alternative name string',
+  SyntaxError);
 E('ERR_TLS_CERT_ALTNAME_INVALID', function(reason, host, cert) {
   this.reason = reason;
   this.host = host;

lib/tls.js

@@ -24,15 +24,22 @@
 const {
   Array,
   ArrayIsArray,
+  ArrayPrototypePush,
+  JSONParse,
   ObjectDefineProperty,
   ObjectFreeze,
+  RegExpPrototypeExec,
   StringFromCharCode,
   StringPrototypeCharCodeAt,
+  StringPrototypeIncludes,
+  StringPrototypeIndexOf,
   StringPrototypeReplace,
   StringPrototypeSplit,
+  StringPrototypeSubstring,
 } = primordials;
 
 const {
+  ERR_TLS_CERT_ALTNAME_FORMAT,
   ERR_TLS_CERT_ALTNAME_INVALID,
   ERR_OUT_OF_RANGE
 } = require('internal/errors').codes;
@@ -217,6 +224,45 @@ function check(hostParts, pattern, wildcards) {
   return true;
 }
 
+// This pattern is used to determine the length of escaped sequences within
+// the subject alt names string. It allows any valid JSON string literal.
+// This MUST match the JSON specification (ECMA-404 / RFC8259) exactly.
+const jsonStringPattern =
+  // eslint-disable-next-line no-control-regex
+  /^"(?:[^"\\\u0000-\u001f]|\\(?:["\\/bfnrt]|u[0-9a-fA-F]{4}))*"/;
+
+function splitEscapedAltNames(altNames) {
+  const result = [];
+  let currentToken = '';
+  let offset = 0;
+  while (offset !== altNames.length) {
+    const nextSep = StringPrototypeIndexOf(altNames, ', ', offset);
+    const nextQuote = StringPrototypeIndexOf(altNames, '"', offset);
+    if (nextQuote !== -1 && (nextSep === -1 || nextQuote < nextSep)) {
+      // There is a quote character and there is no separator before the quote.
+      currentToken += StringPrototypeSubstring(altNames, offset, nextQuote);
+      const match = RegExpPrototypeExec(
+        jsonStringPattern, StringPrototypeSubstring(altNames, nextQuote));
+      if (!match) {
+        throw new ERR_TLS_CERT_ALTNAME_FORMAT();
+      }
+      currentToken += JSONParse(match[0]);
+      offset = nextQuote + match[0].length;
+    } else if (nextSep !== -1) {
+      // There is a separator and no quote before it.
+      currentToken += StringPrototypeSubstring(altNames, offset, nextSep);
+      ArrayPrototypePush(result, currentToken);
+      currentToken = '';
+      offset = nextSep + 2;
+    } else {
+      currentToken += StringPrototypeSubstring(altNames, offset);
+      offset = altNames.length;
+    }
+  }
+  ArrayPrototypePush(result, currentToken);
+  return result;
+}
+
 let urlWarningEmitted = false;
 exports.checkServerIdentity = function checkServerIdentity(hostname, cert) {
   const subject = cert.subject;
@@ -228,7 +274,10 @@ exports.checkServerIdentity = function checkServerIdentity(hostname, cert) {
   hostname = '' + hostname;
 
   if (altNames) {
-    for (const name of altNames.split(', ')) {
+    const splitAltNames = StringPrototypeIncludes(altNames, '"') ?
+      splitEscapedAltNames(altNames) :
+      StringPrototypeSplit(altNames, ', ');
+    for (const name of splitAltNames) {
       if (name.startsWith('DNS:')) {
         dnsNames.push(name.slice(4));
       } else if (name.startsWith('URI:')) {