CVE-2026-45716: Budibase: Builder-to-Admin Privilege Escalation via onboardUsers Endpoint Without SMTP Configuration

The POST /api/global/users/onboard endpoint is protected by workspaceBuilderOrAdmin middleware, allowing any user with builder permissions to access it. When SMTP email is not configured (the default for self-hosted Budibase instances), this endpoint bypasses the admin-restricted invite flow and directly creates users via bulkCreate, accepting arbitrary admin and builder role assignments from the request body. A builder-level user can create a new global admin account and receive the generated password in the response, achieving full privilege escalation.