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Gareth Heyes recently shared a fascinating XSS vector that works exclusively on Safari. The payload leverages Safari’s handling of exceptions when instantiating window.name, which is then passed to eval. Here’s the vector:
<script>onerror = eval,new name</script>
How It Works
1. `onerror = eval` – Sets the global error handler to eval.
2. `new name` – Attempts to instantiate `window.name` as a constructor, which fails since `name` is a string.
3. Safari throws an exception, which is passed to eval, executing arbitrary JavaScript.
You Should Know:
Testing & Exploitation
To test this vulnerability in Safari:
1. Basic PoC:
<script>onerror=alert,new name</script>
This triggers an alert box when the error occurs.
2. Advanced Payload:
<script>onerror=eval,name='alert(document.domain)',new name</script>
This dynamically executes the payload stored in `name`.
Mitigation & Defense
- Content Security Policy (CSP):
Content-Security-Policy: script-src 'self'; object-src 'none';
Prevents inline script execution.
- Sanitization:
Use DOMPurify or similar libraries to filter malicious scripts. Disable
eval:
Avoid using `eval()` in JavaScript to prevent arbitrary code execution.
Browser-Specific Quirks
- Chrome/Firefox: Do not pass the exception to `eval` in the same way.
- Safari: Unique behavior in error handling makes this vector effective.
What Undercode Say
This Safari-specific XSS vector highlights how browser inconsistencies can lead to security vulnerabilities. Developers must:
– Test across multiple browsers.
– Avoid dangerous functions like eval.
– Implement strict CSP headers.
For further reading, check the original post:
Prediction
As browser security evolves, attackers will increasingly target niche engine behaviors. Safari’s unique JavaScript handling may lead to more such exploits in the future.
Expected Output:
<script>onerror=alert,new name</script>
IT/Security Reporter URL:
Reported By: Gareth Heyes – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
