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.

CVE-ID: CVE-2021-44532
PR-URL: https://github.com/nodejs-private/node-private/pull/300
Reviewed-By: Michael Dawson <midawson@redhat.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

1 files changed, 47 insertions, 1 deletions

diff --git a/lib/tls.js b/lib/tls.js
index 683736460b1..eaba340d572 100644
--- a/lib/tls.js
+++ b/lib/tls.js
@@ -30,20 +30,25 @@ const {
   ArrayPrototypePush,
   ArrayPrototypeReduce,
   ArrayPrototypeSome,
+  JSONParse,
   ObjectDefineProperty,
   ObjectFreeze,
+  RegExpPrototypeExec,
   RegExpPrototypeTest,
   StringFromCharCode,
   StringPrototypeCharCodeAt,
   StringPrototypeEndsWith,
   StringPrototypeIncludes,
+  StringPrototypeIndexOf,
   StringPrototypeReplace,
   StringPrototypeSlice,
   StringPrototypeSplit,
   StringPrototypeStartsWith,
+  StringPrototypeSubstring,
 } = primordials;
 
 const {
+  ERR_TLS_CERT_ALTNAME_FORMAT,
   ERR_TLS_CERT_ALTNAME_INVALID,
   ERR_OUT_OF_RANGE
 } = require('internal/errors').codes;
@@ -227,6 +232,45 @@ 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;
+}
+
 exports.checkServerIdentity = function checkServerIdentity(hostname, cert) {
   const subject = cert.subject;
   const altNames = cert.subjectaltname;
@@ -237,7 +281,9 @@ exports.checkServerIdentity = function checkServerIdentity(hostname, cert) {
   hostname = '' + hostname;
 
   if (altNames) {
-    const splitAltNames = StringPrototypeSplit(altNames, ', ');
+    const splitAltNames = StringPrototypeIncludes(altNames, '"') ?
+      splitEscapedAltNames(altNames) :
+      StringPrototypeSplit(altNames, ', ');
     ArrayPrototypeForEach(splitAltNames, (name) => {
       if (StringPrototypeStartsWith(name, 'DNS:')) {
         ArrayPrototypePush(dnsNames, StringPrototypeSlice(name, 4));