Plesk 17.0 through 18.0.31 version, is vulnerable to a Cross-Site Scripting. A malicious subscription owner (either a customer or an additional user), can fully compromise the server if an administrator visits a certain page in Plesk related to the malicious subscription.
https://www.incibe.es/en/incibe-cert/notices/aviso/cross-site-scripting-xss-vulnerability-plesk