[UNIX] XChat /dns Command Execution Vulnerability
From: support@securiteam.comDate: 03/28/02
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From: support@securiteam.com To: list@securiteam.com Date: Thu, 28 Mar 2002 12:55:12 +0100 (CET)
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XChat /dns Command Execution Vulnerability
------------------------------------------------------------------------
SUMMARY
<http://www.xchat.org/> XChat is an IRC client for UNIX operating
systems. I.R.C. is Internet Relay Chat, see <http://irchelp.org>
http://irchelp.org for more information about IRC in general. A security
vulnerability in the product allows attackers to cause the program to
execute arbitrary commands.
DETAILS
There is an issue by the way XChat handle the /exec command, and more
accurately in the /dns command. The /dns should resolve the host of
somebody, by issuing the command "/dns some_nick" and program actually
executes it via string replacement ("%s %s"), where the first string
replaced is the DNS program name (filename), and the second is the
hostname of the person you want to resovle.
Looking into the code of the program, i.e. the cmd_dns() function, you
will find the following around common/outbound.c line 1474
{
sprintf (tbuf, "/exec %s %s", prefs.dnsprogram, nick);
handle_command (tbuf, sess, 0, 0);
}
And far away, at line 1863 in the cmd_exec() function:
execl ("/bin/sh", "sh", "-c", cmd, 0);
No dangerous characters are stripped out of cmd, allowing an attacker to
force a server to respond to DNS query with
";DISPLAY=localhost:0.0;xterm". This would cause the command passed to the
execl function to be as follows: "host;DISPLAY=localhost:0.0;xterm", which
as you probably guessed it will execute an arbitrary command.
To exploit the hole, the attacker would need to force a server to respond
to a whois command with a malformed DNS response.
Migrating factors:
* An attacker must run his own specially patched server.
* An attacker has to cause the user to the /dns command on someone.
ADDITIONAL INFORMATION
The information has been provided by <mailto:spacewalker@altern.org>
SpaceWalker.
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