Cypht before 2.12.2 contains a PHP object injection vulnerability that allows authenticated attackers to execute arbitrary operating system commands by supplying a crafted PHP object graph in the back_query GET parameter of the logout handler. Attackers can pass a base64-encoded serialized payload through this parameter, which is decoded and passed directly to unserialize() without an allow-list, signature check, or type restriction, enabling gadget-chain exploitation to achieve remote code execution as the web server process.

Cypht versions before 2.12.2 are affected by a PHP object injection vulnerability tracked as CVE-2026-71981. Authenticated attackers can exploit the back_query GET parameter in the logout handler by supplying a base64-encoded serialized PHP object payload. The parameter is decoded and passed directly to unserialize() without any allow-list, signature verification, or type restriction. This insecure deserialization enables gadget-chain exploitation, allowing attackers to execute arbitrary operating system commands as the web server process, effectively achieving remote code execution (RCE). The vulnerability requires authentication but poses critical risk due to full RCE potential. A fix was released in Cypht version 2.12.2. Relevant patches and advisories are available via the official GitHub repository and VulnCheck.