Summary Kimai 2.56.0 contains authenticated cross-site request forgery issues in its timesheet state-changing API endpoints. The application reuses the browser's existing session for "/api/*" requests, and both the "stop" and "restart" operations are exposed through "GET" and "PATCH" routes that directly modify business state. As a result, an attacker can trick a logged-in user into visiting a malicious page and cause unauthorized timesheet actions without the victim's consent. Depending on the endpoint, this can stop a running timesheet or create and start a new one from historical data. Details The issue affects at least the following API routes: - "GET /api/timesheets/{id}/stop" - "GET /api/timesheets/{id}/restart" Both routes are non-read-only operations but are still exposed as "GET". In "src/API/TimesheetController.php". A PoC was provided, but removed for security reasons. Impact This vulnerability allows an attacker to trigger unauthorized business-state changes as a logged-in victim. In the validated "stop" case, a running timesheet can be stopped, affecting time tracking integrity and potentially availability of ongoing work tracking. In the "restart" case, a historical timesheet can be restarted and a new record can be created without the victim's knowledge. These actions can corrupt time records, distort billing and reporting, interfere with approvals or audits, and create persistent database-side side effects. Because exploitation requires only that the victim visit a malicious page while authenticated, the attack barrier is low. Solution The "GET" routes were removed, both "stop" and "restart" are only available via "PATCH". See "https://www.kimai.org/en/security/ghsa-r8vr-m544-qh4h" (https://www.kimai.org/en/security/ghsa-r8vr-m544-qh4h) for more information.