PRTG Network Monitor before 18.2.40.1683 allows remote unauthenticated attackers to create users with read-write privileges (including administrator). A remote unauthenticated user can craft an HTTP request and override attributes of the 'include' directive in /public/login.htm and perform a Local File Inclusion attack, by including /api/addusers and executing it. By providing the 'id' and 'users' parameters, an unauthenticated attacker can create a user with read-write privileges (including administrator).
https://www.securityweek.com/cisa-issues-exploitation-warning-for-net-vulnerability/
https://www.ptsecurity.com/ww-en/analytics/threatscape/pt-2018-24/