Improper Authorization in Kimai Timesheet Restart and Duplicate Allows New Timesheets After Project Access Revocation
Summary
Kimai 2.56.0 contains an authenticated authorization bypass in the timesheet restart and duplicate workflows. After a user loses access to a project, the user can still derive a new timesheet from one of their historical entries and create a new record under that now-unauthorized project and activity combination.
This is a permission revocation bypass with persistent write impact. The issue affects both restart and duplicate, which trust ownership of an old timesheet more than the user's current access to the underlying project, activity, and customer.
Details
The issue affects the following operations:
PATCH /api/timesheets/{id}/restartPATCH /api/timesheets/{id}/duplicate
The root cause is that authorization gives too much weight to the fact that the original timesheet belongs to the current user. In src/Voter/TimesheetVoter.php, the *_own_timesheet branch is evaluated before team-based access checks.
The restart/duplicate capability check also verifies only object visibility, not whether the current user still has team-based access to the referenced objects.
In src/API/TimesheetController.php, the restart flow copies the historical project and activity into a new candidate timesheet.
The duplicate flow similarly clones the historical record and saves it.
In src/Timesheet/TimesheetService.php, creation of a new running entry still relies on isGranted('start', $timesheet).
For historical entries that belong to the current user, this logic can still succeed through the *_own_timesheet branch even after project access has been revoked. As a result, normal creation pages correctly stop offering the revoked project, but restart and duplicate can still create new records under it.
The same weakness also affects the Web duplicate flow because the UI path ultimately calls the same save logic in src/Controller/TimesheetAbstractController.php:
*A PoC was provided, but removed for security reasons.*
Impact
This vulnerability allows a user to keep writing new time entries into a project after project access has been revoked. That undermines administrative access-control changes and can pollute project time tracking, budget calculations, statistics, reports, and invoicing workflows.
Because both restart and duplicate can reuse historical project/activity bindings, old timesheet records effectively become reusable capability tokens that survive later access-control changes. This is not a UI artifact or a caching problem: new database rows are persisted after revocation.
Solution
The metoid TimesheetVoter::canStart() now checks team access for project and activity. This verification is used for new timesheets and also for the duplication and restart workflows.
See https://www.kimai.org/en/security/ghsa-c6w6-57jj-62vh for more information.