CodeIgniter is vulnerable to improper authentication via Session Handlers

CodeIgniter is a PHP full-stack web framework. When an application uses (1) multiple session cookies (e.g., one for user pages and one for admin pages) and (2) a session handler is set to `DatabaseHandler`, `MemcachedHandler`, or `RedisHandler`, then if an attacker gets one session cookie (e.g., one for user pages), they may be able to access pages that require another session cookie (e.g., for admin pages). This issue has been patched, please upgrade to version 4.2.11 or later. As a workaround, use only one session cookie.