7.5

CVSS Score

3.1

-

CVSS Score

Basic Information

Concerned about an active attack path?

Talk to our security experts and see Miggo in action.

Miggo Vulnerability Database

→

CVE-2023-48238

CVE-2023-48238: json-web-token library is vulnerable to a JWT algorithm confusion attack

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:

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

Miggo Vulnerability Database

→

CVE-2023-48238

CVE-2023-48238:

7.5

CVSS Score

3.1

-

CVSS Score

Basic Information

Is this CVE running in your environment?

Easily map the attack path and prioritize which CVEs are a threat to your organization

Validate Exposure

Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
json-web-token	npm	<= 3.1.1

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability stems from the decode function's trust in the 'alg' parameter from the unverified JWT header. The library's implementation at index.js:86 uses header.alg to select the verification algorithm without prior validation, violating JWT best practices that require the algorithm to be explicitly specified during verification. This allows attackers to force HMAC verification with a public key (via algorithm substitution) when the server expects RS256 signatures. The provided PoC and advisory both explicitly reference this line/function as the root cause.

Vulnerable functions

Only Mi**o us*rs **n s** t*is s**tion

Vulnerability Intelligence
Miggo AI

Unlock WAF rules for this CVE

Generate vendor-ready rules for the observed attack patterns, plus reasoning and safe deployment guidance

Get WAF rules

WAF Protection Rules

WAF Rule

W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.W** rul*s *v*il**l* *or Mi**o *ustom*rs only.

Reasoning

*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.*v*il**l* *or Mi**o *ustom*rs only.

7.5

-

Basic Information

Basic Information

Concerned about an active attack path?

CVE-2023-48238: json-web-token library is vulnerable to a JWT algorithm confusion attack

Summary

Details

PoC

CVE-2023-48238:

7.5

-

Basic Information

Basic Information

Is this CVE running in your environment?

Technical Details

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

Vulnerable functions

Vulnerability Intelligence
Miggo AI

Unlock WAF rules for this CVE

WAF Protection Rules

WAF Rule

Reasoning

Detect and Respond To Threats Faster.

Technical Details

Basic Information

Basic Information

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

Vulnerable functions

7.5

7.5

CVE-2023-48238: json-web-token library is vulnerable to a JWT algorithm confusion attack

Summary

Details

PoC

Impact

Solution

7.5

-

Basic Information

Basic Information

Concerned about an active attack path?

CVE-2023-48238: json-web-token library is vulnerable to a JWT algorithm confusion attack

Summary

Details

PoC

CVE-2023-48238:

7.5

-

Basic Information

Basic Information

Is this CVE running in your environment?

Technical Details

Technical Details

Vulnerability IntelligenceMiggo AI

Root Cause Analysis

Vulnerable functions

Vulnerability IntelligenceMiggo AI

Unlock WAF rules for this CVE

WAF Protection Rules

WAF Rule

Reasoning

Technical Details

Basic Information

Basic Information

Vulnerability IntelligenceMiggo AI

Root Cause Analysis

Vulnerable functions

7.5

7.5

CVE-2023-48238: json-web-token library is vulnerable to a JWT algorithm confusion attack

Summary

Details

PoC

Impact

Solution

Vulnerability Intelligence
Miggo AI

Vulnerability Intelligence
Miggo AI

Vulnerability Intelligence
Miggo AI