CVE-2026-53595: FreeScout vulnerable to anonymous account takeover via /user-setup empty invite_hash on MySQL

FreeScout is a free help desk and shared inbox built with PHP's Laravel framework. Prior to version 1.8.224, the public endpoint POST /user-setup/{hash}/{invitesentat} (OpenController@userSetupSave) selects the target account solely by its invitehash column, then overwrites that account's email and password and logs in as it. No authentication, cookie, or prior session is required. After a user activates, FreeScout sets invitehash to the empty string. On MySQL and MariaDB, VARCHAR equality ignores trailing spaces, so a single URL-encoded space (%20) matches the stored empty string and selects the lowest-id activated user. The expiry guard decrypts invitesentat with the target's password hash, but Helper::decrypt returns its raw input unchanged when decryption fails. A plaintext numeric value such as 9999999999 therefore passes the time-to-live check without any secret. The result is that an anonymous attacker sets the email and password of the lowest-id activated FreeScout account (a support agent, or an administrator if one was added by invitation) and authenticates as that account. Version 1.8.224 contains a fix.