The ProfileGrid WordPress plugin before 5.9.9.7 does not perform any authorization or ownership check on some of its private-message thread actions, allowing authenticated users with Subscriber-level access and above to soft-delete, tamper with the metadata of, and mark as read other users' private message threads.
https://wpscan.com/vulnerability/7368fe32-9415-47c3-b94b-b85ca1a0d101/