CVE-2025-65328 is a security vulnerability identified in Mega-Fence's webgate-lib component, specifically in versions 25.1.914 and earlier. The vulnerability arises because the software trusts the first IP address value in the X-Forwarded-For (XFF) HTTP header as the true client IP without validating whether the request passed through a trusted proxy chain. The XFF header is commonly used to identify the originating IP address of a client connecting through one or more proxies. However, if the application blindly trusts the first IP in the header, an attacker can craft a request with a spoofed XFF header to impersonate any IP address. This spoofed IP is then used in security-sensitive contexts, such as setting the WG_CLIENT_IP cookie, which may be used for IP-based allowlisting or access control decisions. As a result, attackers can bypass IP-based restrictions, gaining unauthorized access or evading detection. The vulnerability does not require authentication or user interaction, making it easier to exploit remotely. No public exploits are known at this time, but the flaw represents a significant risk in environments relying on IP-based security controls without proper proxy validation. The root cause is the lack of validation of the proxy chain to confirm that the XFF header can be trusted. Proper mitigation involves verifying that the request passed through trusted proxies before accepting the first IP in the XFF header as legitimate. This vulnerability highlights the importance of correctly handling proxy headers in web applications and infrastructure components.

For European organizations, the impact of CVE-2025-65328 can be substantial, especially for those relying on IP-based allowlists or access controls in their web infrastructure. Attackers can spoof trusted IP addresses to bypass security controls, potentially gaining unauthorized access to sensitive systems or data. This can lead to data breaches, unauthorized actions, or evasion of monitoring and logging mechanisms. Critical sectors such as finance, healthcare, government, and critical infrastructure that use Mega-Fence or similar proxy-based architectures are particularly at risk. The vulnerability undermines the integrity of client IP identification, which is fundamental for enforcing network security policies, auditing, and incident response. Additionally, organizations using the WG_CLIENT_IP cookie or similar mechanisms for session management or security decisions may face session hijacking or privilege escalation risks. The absence of known exploits currently limits immediate widespread impact, but the vulnerability presents a clear vector for attackers to exploit once weaponized. Overall, the threat could compromise confidentiality, integrity, and availability of affected systems if exploited.

To mitigate CVE-2025-65328, European organizations should implement the following specific measures: 1) Configure Mega-Fence webgate-lib and any proxy or web application firewall to validate the entire proxy chain and only trust XFF headers from known, trusted proxies. 2) Avoid relying solely on the first IP address in the XFF header for security decisions; instead, use server-side logic to parse and verify the header against trusted proxy IPs. 3) Where possible, disable or restrict the use of client-supplied XFF headers and enforce strict proxy configurations that strip or overwrite untrusted headers. 4) Review and update IP-based allowlists and access controls to incorporate additional factors beyond client IP, such as authentication tokens or client certificates. 5) Monitor logs for anomalous or suspicious XFF header values that could indicate attempted spoofing. 6) Apply any available patches or updates from Mega-Fence once released, and maintain an inventory of affected versions to prioritize remediation. 7) Conduct security testing and penetration testing focused on header spoofing and proxy validation to identify weaknesses. These steps go beyond generic advice by focusing on proxy chain validation and header trust boundaries, which are critical to preventing exploitation of this vulnerability.