Python Social Auth is a social authentication/registration mechanism. Prior to version 5.0.0, the "vk-app" backend accepted VK application callback data without verifying the callback signature when the "auth_key" parameter was omitted. Applications using this backend could treat unsigned attacker-controlled data as a verified VK identity. An attacker could choose callback fields such as "viewer_id", "access_token", "api_id", and "api_result", potentially allowing authentication as an arbitrary VK user ID. The issue affects only applications using the "vk-app" backend. The issue has been fixed in version 5.0.0 by requiring "auth_key" to be present and valid before callback data is trusted.