Webmin through 1.991, when the Authentic theme is used, allows remote code execution when a user has been manually created (i.e., not created in Virtualmin or Cloudmin). This occurs because settings-editor_write.cgi does not properly restrict the file parameter.
https://www.twitch.tv/videos/1483029790
https://webmin.com/changes.html
https://github.com/webmin/webmin/releases
https://github.com/webmin/webmin/issues/1635
https://github.com/webmin/webmin/commit/6a2334bf8b27d55c7edf0b2825cd14f3f8a69d4d
https://github.com/webmin/authentic-theme/releases
https://github.com/esp0xdeadbeef/rce_webmin/blob/main/exploit.py