CVE-2025-52186 is a Server-Side Request Forgery (SSRF) vulnerability identified in the Lichess lila platform prior to commit 11b4c0fb00f0ffd823246f839627005459c8f05c, disclosed in November 2025. The vulnerability resides in the game export API, specifically in the handling of the 'players' parameter. This parameter is passed directly to an internal HTTP client without any validation or sanitization, enabling an attacker to supply arbitrary URLs. Consequently, the server can be manipulated to send HTTP requests to internal or external systems chosen by the attacker. SSRF vulnerabilities like this can be exploited to access internal network resources that are otherwise inaccessible, potentially leading to information disclosure, port scanning of internal networks, or triggering actions on internal services. The CVSS 3.1 base score is 6.5 (medium), reflecting that the attack vector is network-based (AV:N), requires no privileges (PR:N), no user interaction (UI:N), and impacts confidentiality (C:L) and availability (A:L) but not integrity. No known public exploits have been reported yet, but the vulnerability's presence in a popular open-source chess platform used globally, including Europe, raises concerns. The lack of authentication requirements and the direct use of user-supplied input in server-side HTTP requests make this vulnerability a significant risk if left unaddressed.

For European organizations, the SSRF vulnerability in Lichess lila could lead to unauthorized internal network reconnaissance or access to sensitive internal services that are not exposed externally. This could result in partial confidentiality loss if internal endpoints return sensitive data or metadata. Additionally, attackers might leverage the SSRF to cause denial of service by overwhelming internal services or triggering unintended actions. Organizations hosting Lichess instances or integrating its APIs could see disruption or data leakage. Given the popularity of Lichess in Europe, particularly among educational institutions, chess clubs, and online communities, the risk extends to both private and public sector entities. The medium severity indicates that while the vulnerability is exploitable remotely without authentication, the impact is somewhat limited to confidentiality and availability, with no direct integrity compromise. However, SSRF can be a stepping stone for more complex attacks, especially if combined with other vulnerabilities or misconfigurations in internal networks.

To mitigate CVE-2025-52186, organizations should immediately update Lichess lila to the fixed version post commit 11b4c0fb00f0ffd823246f839627005459c8f05c once available. In the interim, implement strict input validation and sanitization on the 'players' parameter to ensure only expected and safe URLs or identifiers are accepted. Employ allowlisting for outbound HTTP requests initiated by the server, restricting them to known safe destinations. Network segmentation and firewall rules should be enforced to limit the server's ability to reach sensitive internal services. Monitoring and logging outbound HTTP requests from the Lichess server can help detect anomalous activity indicative of SSRF exploitation attempts. Additionally, consider deploying Web Application Firewalls (WAFs) with rules tailored to detect and block SSRF patterns. Regular security assessments and penetration testing focused on SSRF vectors are recommended to identify and remediate similar issues proactively.