Summary

The administrative proxy route (cmsproxy) in Aimeos Pagible CMS is vulnerable to a Server-Side Request Forgery (SSRF) attack via DNS Rebinding. A Time-of-Check to Time-of-Use (TOCTOU) race condition exists between the URL validation phase and the actual HTTP request phase, allowing attackers to access internal network resources and cloud metadata endpoints.

Details

Before executing an HTTP request to fetch external content, the AdminController::proxy controller validates the target URL using \Aimeos\Cms\Utils::isValidUrl($url). This function performs a DNS query to verify that the hostname does not resolve to private or reserved IP ranges (e.g., 127.0.0.1, 10.0.0.0/8, 169.254.169.254).

If the validation passes, the application proceeds to the "Use" phase, invoking Guzzle/cURL to send the request. However, Guzzle performs a second DNS lookup to establish the socket connection.

An attacker can exploit this by setting up a malicious DNS server for a domain they control and configuring it with a TTL of 0.

1. During the validation "Check", the DNS server returns a safe, public IP.
2. During the Guzzle "Use", the DNS server returns an internal/private IP.

POC

1. Attacker registers `rebound.test.com with a custom nameserver.
2. Attacker generates a valid proxy token (assuming basic authenticated access).
3. Attacker requests /cmsproxy?url=http://rebound.test.com.
4. isValidUrl checks rebound.test.com. DNS returns 8.8.8.8. Validation passes.
5. Guzzle requests http://rebound.test.com. DNS returns 169.254.169.254.
6. The CMS fetches AWS Instance Metadata and returns it to the attacker.

References

• GHSA-mmj8-wcvw-6789