Authentication Bypass Vulnerability in Admidio Forum Module

Admidio versions prior to 5.0.11 are susceptible to an authentication bypass vulnerability within the forum module. This flaw manifests when the application is configured in 'login-only' mode. The access control logic implemented in 'modules/forum.php' fails to correctly validate the authentication state before serving content. Consequently, unauthenticated attackers can craft requests to the forum module using specific read-only parameters to access and exfiltrate forum topics and user posts. This vulnerability (CVE-2026-69091) poses a significant risk to organizations relying on Admidio for internal or sensitive community communications, as it allows for unauthorized data access without requiring valid credentials.

Attack Chain

1. Attacker performs reconnaissance to identify Admidio instances configured in 'login-only' mode.
2. Attacker probes the target web application to verify the presence of the 'modules/forum.php' endpoint.
3. Attacker crafts an HTTP request targeting 'modules/forum.php' while ensuring the application context triggers the vulnerable logic path.
4. Attacker injects specific read-only parameters into the request query or body to bypass existing access controls.
5. The server-side code in 'modules/forum.php' fails to verify the attacker's session or authentication status.
6. The server processes the request and returns the requested forum topics and posts in the HTTP response.
7. The attacker iterates through available forum threads to perform unauthorized data exfiltration.

Impact

Successful exploitation allows an unauthenticated attacker to view private forum topics and user posts that were intended to be restricted to logged-in users. This results in the unauthorized exposure of sensitive internal communications or community data.

Recommendation

Prioritized actions for detection and remediation:

• Upgrade Admidio instances to version 5.0.11 or later immediately to patch the vulnerable access control logic in 'modules/forum.php'.
• Deploy the provided web server detection rule to identify attempted exploitation of CVE-2026-69091.
• Review web server access logs for anomalous, high-volume requests directed at 'modules/forum.php' from external IP addresses.