CVE-2025-66571 is a critical vulnerability classified under CWE-502 (Deserialization of Untrusted Data) affecting UNA CMS, a PHP-based content management system widely used for social networking and community websites. The flaw exists in the file BxBaseMenuSetAclLevel.php, where the profile_id POST parameter is passed directly to PHP's unserialize() function without proper validation or sanitization. This unsafe deserialization allows remote attackers to craft malicious serialized PHP objects and send them via POST requests to the vulnerable endpoint. Because the vulnerability requires no authentication or user interaction, attackers can exploit it remotely to inject arbitrary PHP objects. This can lead to PHP object injection attacks, enabling arbitrary code execution on the server, potentially resulting in full system compromise. The vulnerability affects UNA CMS versions from 9.0.0-RC1 up to 14.0.0-RC4. The CVSS 4.0 base score is 9.3, reflecting the vulnerability's ease of exploitation (network vector, no privileges or user interaction required) and its severe impact on confidentiality, integrity, and availability. Although no public exploits have been reported yet, the nature of the vulnerability makes it a prime target for attackers. The lack of official patches at the time of disclosure increases the urgency for organizations to apply mitigations or upgrade once fixes become available.

For European organizations, the impact of CVE-2025-66571 can be severe, especially for those relying on UNA CMS to host community-driven or social networking platforms. Successful exploitation can lead to complete server takeover, exposing sensitive user data, intellectual property, and internal communications. This can result in data breaches, defacement, service disruption, and reputational damage. Given the unauthenticated and remote exploitability, attackers can rapidly compromise multiple instances across organizations. The vulnerability also poses risks to compliance with GDPR and other data protection regulations due to potential unauthorized data access and processing. Organizations operating critical community services or platforms with high user engagement are particularly vulnerable to targeted attacks leveraging this flaw.

Immediate mitigation steps include restricting access to the vulnerable endpoint by implementing web application firewall (WAF) rules that block or sanitize POST requests containing serialized data in the profile_id parameter. Organizations should monitor web server logs for suspicious unserialize attempts and anomalous POST requests. Until an official patch is released, disabling or restricting the functionality invoking unserialize() on untrusted input is recommended. Upgrading UNA CMS to a fixed version as soon as it becomes available is critical. Additionally, applying PHP hardening techniques such as disabling dangerous functions (e.g., unserialize) or using safer serialization alternatives can reduce risk. Regular security audits and penetration testing focused on deserialization vulnerabilities should be conducted. Organizations should also implement strict input validation and employ runtime application self-protection (RASP) solutions to detect and block exploitation attempts in real time.