Wekan is an open source kanban tool built with Meteor. Versions 8.32 and 8.33 have a critical Insecure Direct Object Reference (IDOR) issue which could allow unauthorized users to modify custom fields across boards through its custom fields update endpoints, potentially leading to unauthorized data manipulation. The PUT /api/boards/:boardId/custom-fields/:customFieldId endpoint in Wekan validates that the authenticated user has access to the specified boardId, but the subsequent database update uses only the custom field's _id as a filter without confirming the field actually belongs to that board. This means an attacker who owns any board can modify custom fields on any other board by supplying a foreign custom field ID, and the same flaw exists in the POST, PUT, and DELETE endpoints for dropdown items under custom fields. The required custom field IDs can be obtained by exporting a board (which only needs read access), since the exported JSON includes the IDs of all board components. The authorization check is performed against the wrong resource, allowing cross-board custom field manipulation. This issue has been fixed in version 8.34.