Webmin 1.973 is affected by Cross Site Request Forgery (CSRF) to create a privileged user through Webmin's add users feature, and then get a reverse shell through Webmin's running process feature.
Arbitrary command execution can occur in Webmin through 1.962. Any user authorized for the Package Updates module can execute arbitrary commands with root privileges via vectors involving %0A and %0C. NOTE: this issue exists because of an incomplete fix for CVE-2019-12840.