Budibase versions before 3.40.0 contain an authorization/authentication bypass in the PUT /api/global/users/tenant/owner (changeTenantOwnerEmail) endpoint. On self-hosted instances (SELF_HOSTED or DISABLE_ACCOUNT_PORTAL set), the cloudRestricted middleware is a no-op and the route is protected only by a general authentication check, so any authenticated user — including a lowest-privilege BASIC app user — can reassign the tenant account-holder (top-privilege admin) email to an attacker-controlled address. The attacker can then use the public password-reset flow to take over the admin account, leading to full administrative access.