CVE-2026-48085: falha crítica em open-reception appointment-booking-software

OpenReception's appointment booking software provides an end-to-end encrypted appointment booking platform. Prior to version 1.0.1, a fully provisioned OpenReception instance accepts unauthenticated POST requests to `/setup/create-admin-account` and creates additional GLOBAL_ADMIN accounts without verifying that an admin already exists. Any unauthenticated network attacker who can submit a same-origin form POST gains full platform-level administrative control. The newly created account is `is_active=true` with `confirmation_state=ACCESS_GRANTED` and does not require completing email confirmation; the GLOBAL_ADMIN row is created active and immediately usable. Login and tenant enumeration succeed without any further interaction. This is distinct from the deployment race condition already documented on the `Claiming an instance` page. That documented race covers the window between deployment and first claim. The bug reported here works after the operator has properly claimed and configured the instance: the layout-level guard that protects the setup page only redirects on GET, while the `default` form action handler creates the user without rechecking `adminExists()`. Three GLOBAL_ADMIN accounts were created in succession during testing, with no rate limiting observed. Audit-specific event logging beyond standard application logs was not assessed; the standard `[error]` line that surfaces only when a uniqueness conflict is hit is not the same as a security event for "additional admin created post-claim". The form post is rejected for browser drive-by CSRF by SvelteKit's built-in same-origin check, but any tool that supplies a matching `Origin` header (curl, Burp, automated scanners, server-side proxies) bypasses this trivially. No additional preconditions exist. Users should upgrade to version 1.0.1 to receive a patch.