CVE-2025-66508 is a medium-severity authentication bypass vulnerability affecting 1Panel, an open-source web-based control panel for Linux server management. Versions prior to 2.0.14 use the Gin web framework's default trusted proxy configuration, which trusts all IP addresses (TrustedProxies = 0.0.0.0/0). This misconfiguration allows any client to spoof the X-Forwarded-For HTTP header to impersonate any IP address, including localhost (127.0.0.1) or other IPs whitelisted by IP-based access controls such as AllowIPs or API whitelists. Since 1Panel relies on the ClientIP() function for enforcing these IP-based restrictions, attackers can bypass these controls without authentication or user interaction simply by sending a crafted header. This effectively nullifies all IP-based security mechanisms, potentially allowing unauthorized access to administrative functions or sensitive server management capabilities. The vulnerability does not impact availability but can compromise confidentiality and integrity by granting unauthorized access. The issue was fixed in version 2.0.14 by correcting the trusted proxy configuration to restrict which IPs are considered proxies. No known exploits have been reported in the wild as of the publication date. The vulnerability is tracked under CWE-290 (Authentication Bypass by Spoofing) and has a CVSS v3.1 base score of 6.5, reflecting network attack vector, low attack complexity, no privileges or user interaction required, and partial confidentiality and integrity impact.

For European organizations using 1Panel versions below 2.0.14, this vulnerability poses a significant risk of unauthorized access to Linux server management interfaces. Attackers can bypass IP-based access controls designed to restrict administrative access, potentially leading to unauthorized configuration changes, data exposure, or lateral movement within networks. This could impact confidentiality and integrity of critical systems managed via 1Panel. The vulnerability does not directly affect availability but could facilitate further attacks that do. Organizations in sectors with high reliance on Linux servers and web-based management tools—such as finance, telecommunications, government, and critical infrastructure—face elevated risks. The ease of exploitation without authentication or user interaction increases the threat level. Although no exploits are known in the wild yet, the widespread use of 1Panel in European data centers and hosting providers could make this an attractive target for attackers seeking footholds in enterprise environments.

The primary mitigation is to upgrade all affected 1Panel installations to version 2.0.14 or later, which corrects the trusted proxy configuration to prevent arbitrary IP spoofing via the X-Forwarded-For header. Until upgrades can be applied, organizations should consider implementing network-level controls to restrict access to 1Panel interfaces to trusted IP ranges and avoid exposing the management panel to the public internet. Additionally, web application firewalls (WAFs) can be configured to detect and block suspicious X-Forwarded-For header manipulations. Monitoring access logs for anomalous IP header usage and unauthorized access attempts is recommended. Organizations should review and tighten any IP-based access control policies and consider multi-factor authentication for administrative access to reduce reliance on IP filtering alone. Finally, conducting internal audits to identify all 1Panel instances and verifying their versions will help ensure comprehensive remediation.