Skip failed public key parse for HMAC string secrets

test/issue_1046.tests.js

@@ -0,0 +1,23 @@
+const jwt = require('../index');
+const crypto = require('crypto');
+const assert = require('chai').assert;
+const expect = require('chai').expect;
+const JsonWebTokenError = require('../lib/JsonWebTokenError');
+
+describe('issue 1046', function () {
+  it('verifies HS256 tokens signed with a string secret', function () {
+    const secret = 'a-shared-secret-of-reasonable-length';
+    const token = jwt.sign({ sub: 'u' }, secret, { algorithm: 'HS256' });
+    const decoded = jwt.verify(token, secret, { algorithms: ['HS256'] });
+    assert.equal(decoded.sub, 'u');
+  });
+
+  it('still rejects HMAC verification with a PEM public key', function () {
+    const { publicKey } = crypto.generateKeyPairSync('rsa', { modulusLength: 2048 });
+    const pem = publicKey.export({ type: 'spki', format: 'pem' });
+    const maliciousToken = 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6InJzYUtleUlkIn0.eyJmb28iOiJiYXIiLCJpYXQiOjE2NTk1MTA2MDh9.cOcHI1TXPbxTMlyVTfjArSWskrmezbrG8iR7uJHwtrQ';
+
+    expect(() => jwt.verify(maliciousToken, pem, { algorithms: ['RS256', 'HS256'] }))
+      .to.throw(JsonWebTokenError, 'must be a symmetric key');
+  });
+});

verify.js

@@ -18,6 +18,15 @@ if (PS_SUPPORTED) {
   RSA_KEY_ALGS.splice(RSA_KEY_ALGS.length, 0, 'PS256', 'PS384', 'PS512');
 }
 
+// PEM/SSH/JWK material must still go through createPublicKey first so an HS*
+// token cannot treat an RSA public key as an HMAC secret.
+function looksLikeAsymmetricKey(key) {
+  if (typeof key !== 'string') {
+    return true;
+  }
+  return /^\s*(-----BEGIN |ssh-|\{)/.test(key);
+}
+
 module.exports = function (jwtString, secretOrPublicKey, options, callback) {
   if ((typeof options === 'function') && !callback) {
     callback = options;
@@ -118,11 +127,16 @@ module.exports = function (jwtString, secretOrPublicKey, options, callback) {
     }
 
     if (secretOrPublicKey != null && !(secretOrPublicKey instanceof KeyObject)) {
+      const trySecretFirst = !looksLikeAsymmetricKey(secretOrPublicKey);
       try {
-        secretOrPublicKey = createPublicKey(secretOrPublicKey);
+        secretOrPublicKey = trySecretFirst
+          ? createSecretKey(typeof secretOrPublicKey === 'string' ? Buffer.from(secretOrPublicKey) : secretOrPublicKey)
+          : createPublicKey(secretOrPublicKey);
       } catch (_) {
         try {
-          secretOrPublicKey = createSecretKey(typeof secretOrPublicKey === 'string' ? Buffer.from(secretOrPublicKey) : secretOrPublicKey);
+          secretOrPublicKey = trySecretFirst
+            ? createPublicKey(secretOrPublicKey)
+            : createSecretKey(typeof secretOrPublicKey === 'string' ? Buffer.from(secretOrPublicKey) : secretOrPublicKey);
         } catch (_) {
           return done(new JsonWebTokenError('secretOrPublicKey is not valid key material'))
         }