Homarr has a Race Condition in Invite Token Registration (TOCTOU)

Homarr is an open-source dashboard. Prior to 1.57.0, the user registration endpoint (/api/trpc/user.register) is vulnerable to a race condition that allows an attacker to create multiple user accounts from a single-use invite token. The registration flow performs three sequential database operations without a transaction: CHECK, CREATE, and DELETE. Because these operations are not atomic, concurrent requests can all pass the validation step (1) before any of them reaches the deletion step (3). This allows multiple accounts to be registered using a single invite token that was intended to be single-use. This vulnerability is fixed in 1.57.0.