FreeScout: Thread Edit Authorization Bypass via Missing Mailbox Check

FreeScout is a free help desk and shared inbox built with PHP's Laravel framework. Prior to 1.8.221, while investigating the ThreadPolicy::delete issue reported previously, the same missing mailbox membership check was found in the sibling ThreadPolicy::edit method. A user with the PERM_EDIT_CONVERSATIONS permission who created a message or internal note in Mailbox A can rewrite that thread's body after an administrator removes them from Mailbox A, because the policy checks only authorship and a global permission flag — not current mailbox membership. This vulnerability is fixed in 1.8.221.