Kimai before 2.56.0 does not enforce team-membership checks in TimesheetVoter::voteOnAttribute(), which maps permissions only to own_timesheet or other_timesheet. As a result, any authenticated user with ROLE_TEAMLEAD (or a role holding edit_other_timesheet/delete_other_timesheet) can read, modify, and permanently delete timesheets belonging to any user system-wide via the API, regardless of team membership. Timesheet IDs are sequential integers and trivially enumerable. ROLE_USER accounts are correctly restricted. (Note: the maintainers characterize this behavior as matching the documented permission model.)

Kimai versions before 2.56.0 contain an authorization bypass vulnerability in TimesheetVoter::voteOnAttribute() that fails to enforce team-membership checks. The function maps permissions solely to own_timesheet or other_timesheet without verifying team relationships. Any authenticated user with ROLE_TEAMLEAD or roles granting edit_other_timesheet/delete_other_timesheet can read, modify, and permanently delete any user's timesheets system-wide via the API. Timesheet IDs are sequential integers, making enumeration trivial for attackers. ROLE_USER accounts are correctly restricted and not affected. The vulnerability was fixed in Kimai 2.56.0. The maintainers have noted this behavior aligns with their documented permission model, though it presents a significant access control risk in multi-team environments.