Plane is an open-source project management tool. In 1.3.1 and earlier, ProjectMemberViewSet.partial_update places its authorization checks inside the role update branch, so a guest or member can omit role and change another ProjectMember record's is_active field, including deactivating a project administrator. ProjectMemberPreferenceEndpoint.patch separately trusts the member_id path value and lets a project member overwrite another member's preferences. These missing object-level authorization checks permit membership disruption and cross-member preference tampering. The vulnerability is fixed in 1.4.0.