CVE-2026-11102 – OAuth2 Implicit Grant Fragment Hijacking

Program Code (Node.js + Exploit)

// oauth_server.js - OAuth2 provider issuing tokens in fragment
const express = require('express');
const app = express();

app.get('/authorize', (req, res) => {
    const redirectUri = req.query.redirect_uri;
    const state = req.query.state || '';
    // Simulate user approval: redirect with access token in fragment
    const token = 'secret_access_token';
    res.redirect(`${redirectUri}#access_token=${token}&state=${state}`);
});

app.listen(3000, () => console.log('OAuth server on :3000'));

CVE-2026-11102 – OAuth2 Implicit Grant Fragment Hijacking

Overview

An OAuth2 provider implements the implicit grant flow without validating the redirect_uri against a whitelist. An attacker can supply a malicious URI and, after the user authenticates, the access token is leaked via the URL fragment to the attacker’s page.

Vulnerability Details

• Type: Insecure Direct Object Reference / Redirect URI Validation
• Impact: Account takeover via stolen access token.
• Root Cause: The authorization server does not validate that the redirect_uri exactly matches a pre-registered value, allowing redirection to an attacker-controlled domain.

Exploit Demonstration

1. Start the OAuth server:
   root@kitploit:~

   npm install express
   node oauth_server.js
   

2. Run the exploit:
   root@kitploit:~

   python exploit_fragment_hijack.py