Plane is an open-source project management tool. Prior to 1.3.0, the ProjectMemberViewSet.partial_update method allows any project member, including a user with the lowest GUEST role, to modify another project member's role. The authorization check prevents assigning a role higher than the requester's role but does not prevent assigning a lower or equal role, allowing a Guest to demote Administrators and Members and deny them project control. This vulnerability is fixed in 1.3.0.