CVE-2025-65328 is a vulnerability in Mega-Fence's webgate-lib component (version 25.1.914 and prior) that arises from improper validation of the X-Forwarded-For (XFF) HTTP header. The software trusts the first IP address in the XFF header as the true client IP without verifying whether the request passed through trusted proxies. This lack of validation allows an attacker to craft a request with a spoofed XFF header, causing the system to incorrectly identify the attacker-controlled IP as the client IP. This spoofed IP is then propagated into security-relevant state, such as the WG_CLIENT_IP cookie, which may be used for IP-based allowlists or other access control mechanisms. Because the system does not authenticate or validate the proxy chain, attackers can bypass IP allowlists that rely on the client IP for filtering. The vulnerability is classified under CWE-807 (Reliance on Untrusted Inputs in a Security Decision). The CVSS v3.1 base score is 6.5, reflecting network attack vector, low attack complexity, no privileges or user interaction required, and limited confidentiality and integrity impact without availability impact. No patches or known exploits are currently reported, but the vulnerability poses a risk to deployments relying on IP-based security controls.

For European organizations, this vulnerability can undermine security controls that depend on accurate client IP identification, such as IP allowlists, geofencing, and rate limiting. Attackers can bypass these controls by spoofing the XFF header, potentially gaining unauthorized access or evading detection. This is particularly concerning for organizations in sectors like finance, government, and critical infrastructure that often rely on IP-based restrictions. The integrity of security logs and audit trails may also be compromised, affecting incident response and forensic investigations. While the vulnerability does not directly impact availability, the loss of trust in client IP data can lead to broader security risks and compliance issues under regulations like GDPR if unauthorized access occurs.

Organizations should implement strict validation of the X-Forwarded-For header by verifying that the request has passed through trusted proxies before trusting the client IP value. This can be achieved by configuring Mega-Fence or the web server to only accept XFF headers from known proxy IP addresses. Additionally, consider using alternative methods for client identification, such as mutual TLS or token-based authentication, rather than relying solely on IP allowlists. Network-level protections like Web Application Firewalls (WAFs) can be configured to detect and block suspicious or malformed XFF headers. Regularly update Mega-Fence to the latest version once a patch is released. Finally, audit and monitor logs for anomalies in client IP addresses and review access control policies to reduce reliance on IP-based filtering alone.