An Improper Data Validation Vulnerability exists in Webmin 1.941 and earlier affecting the Command Shell Endpoint. A user may enter HTML code into the Command field and submit it. Then, after visiting the Action Logs Menu and displaying logs, the HTML code will be rendered (however, JavaScript is not executed). Changes are kept across users.
rpc.cgi in Webmin through 1.920 allows authenticated Remote Code Execution via a crafted object name because unserialise_variable makes an eval call. NOTE: the Webmin_Servers_Index documentation states "RPC can be used to run any command or modify any file on a server, which is why access to it must not be granted to un-trusted Webmin users."
In Webmin through 1.910, any user authorized to the "Package Updates" module can execute arbitrary commands with root privileges via the data parameter to update.cgi.
Webmin 1.890 has XSS via /config.cgi?webmin, the /shell/index.cgi history parameter, /shell/index.cgi?stripped=1, or the /webminlog/search.cgi uall or mall parameter.
Webmin 1.900 allows remote attackers to execute arbitrary code by leveraging the "Java file manager" and "Upload and Download" privileges to upload a crafted .cgi file via the /updown/upload.cgi URI.
An issue was discovered in Webmin 1.840 and 1.880 when the default Yes setting of "Can view any file as a log file" is enabled. As a result of weak default configuration settings, limited users have full access rights to the underlying Unix system files, allowing the user to read sensitive data from the local system (using Local File Include) such as the '/etc/shadow' file via a "GET /syslog/save_log.cgi?view=1&file=/etc/shadow" request.
custom/run.cgi in Webmin before 1.870 allows remote authenticated administrators to conduct XSS attacks via the description field in the custom command functionality.