From 32a731dcf166a28aa3760de5ca567d1e89da1f61 Mon Sep 17 00:00:00 2001
From: Bruno Peralva <brunoperalva@hotmail.com>
Date: Thu, 15 Oct 2026 10:50:44 -0300
Subject: [PATCH] fix(verify): surface key parsing error for malformed PEM
 public keys

A malformed PEM key passed to verify() fell back to being treated as an
HMAC secret, which then failed with a misleading "invalid algorithm"
error. Now, when the key material looks like PEM and createPublicKey()
fails, verify() returns a JsonWebTokenError carrying the crypto error.

Fixes #882
---
 test/verify.tests.js | 31 +++++++++++++++++++++++++++++++
 verify.js            |  9 ++++++++-
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/test/verify.tests.js b/test/verify.tests.js
index 88500756..59467b4e 100644
--- a/test/verify.tests.js
+++ b/test/verify.tests.js
@@ -30,6 +30,37 @@ describe('verify', function() {
     });
   });
 
+  describe('with a malformed PEM public key', function () {
+    const token = jwt.sign({ foo: 'bar' }, priv, { algorithm: 'RS256' });
+    const malformedPem = pub.toString().replace(/\n[A-Za-z0-9+/]{10}/, '\n');
+
+    it('should report the key parsing error instead of "invalid algorithm"', function () {
+      let error;
+      try {
+        jwt.verify(token, malformedPem);
+      } catch (e) {
+        error = e;
+      }
+      expect(error).to.be.instanceOf(JsonWebTokenError);
+      expect(error.message).to.match(/^secretOrPublicKey is not a valid PEM key: /);
+      expect(error.inner).to.be.instanceOf(Error);
+    });
+
+    it('should report the key parsing error when the key is a Buffer', function () {
+      expect(function () {
+        jwt.verify(token, Buffer.from(malformedPem));
+      }).to.throw(JsonWebTokenError, /secretOrPublicKey is not a valid PEM key/);
+    });
+
+    it('should report the key parsing error to the callback', function (done) {
+      jwt.verify(token, malformedPem, function (err) {
+        expect(err).to.be.instanceOf(JsonWebTokenError);
+        expect(err.message).to.match(/secretOrPublicKey is not a valid PEM key/);
+        done();
+      });
+    });
+  });
+
   it('should not be able to verify unsigned token', function () {
     const header = { alg: 'none' };
     const payload = { iat: Math.floor(Date.now() / 1000 ) };
diff --git a/verify.js b/verify.js
index cdbfdc45..77e6db14 100644
--- a/verify.js
+++ b/verify.js
@@ -18,6 +18,10 @@ if (PS_SUPPORTED) {
   RSA_KEY_ALGS.splice(RSA_KEY_ALGS.length, 0, 'PS256', 'PS384', 'PS512');
 }
 
+function looksLikePem(key) {
+  return (typeof key === 'string' || Buffer.isBuffer(key)) && key.includes('-----BEGIN');
+}
+
 module.exports = function (jwtString, secretOrPublicKey, options, callback) {
   if ((typeof options === 'function') && !callback) {
     callback = options;
@@ -120,7 +124,10 @@ module.exports = function (jwtString, secretOrPublicKey, options, callback) {
     if (secretOrPublicKey != null && !(secretOrPublicKey instanceof KeyObject)) {
       try {
         secretOrPublicKey = createPublicKey(secretOrPublicKey);
-      } catch (_) {
+      } catch (err) {
+        if (looksLikePem(secretOrPublicKey)) {
+          return done(new JsonWebTokenError('secretOrPublicKey is not a valid PEM key: ' + err.message, err));
+        }
         try {
           secretOrPublicKey = createSecretKey(typeof secretOrPublicKey === 'string' ? Buffer.from(secretOrPublicKey) : secretOrPublicKey);
         } catch (_) {