The User Frontend WordPress plugin before 4.3.11 does not prevent user-supplied field values from being deserialized when a submitted post is reopened in its frontend editing form, allowing authenticated users with subscriber-level access and above to perform PHP Object Injection, which may lead to remote code execution when a suitable gadget chain is present on the site.
https://wpscan.com/vulnerability/019d83bd-24d3-4575-9d0b-55f75fdb0bfa/