InvoiceShelf is an open-source web & mobile app that helps track expenses, payments and create professional invoices and estimates. Prior to version 2.4.1, in InvoiceShelf's multi-company installations, any user who is an Owner of one company can read and overwrite any user account in any other company on the same installation. `GET/PUT /api/v1/users/{user}` resolves the target `User` by global primary key, and `UserPolicy` checks only that the requester owns their own header-company — it never verifies that the target user belongs to that company. This allows cross-tenant disclosure of user data and full account takeover (email/password overwrite + company re-assignment). Version 2.4.1 fixes the issue.