oss-security - CVE-2013-1436: xmonad-contrib remote command injection

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Message-ID: <20130726141637.GA15592@hesperos>
Date: Fri, 26 Jul 2013 11:16:37 -0300
From: Raúl Benencia <rul@...gan.cc>
To: oss-security@...ts.openwall.com
Cc: Joachim Breitner <nomeata@...ian.org>, security@...ian.org,
	adam vogt <vogt.adam@...il.com>
Subject: CVE-2013-1436: xmonad-contrib remote command injection

Hello,

I've discovered a remote command injection vulnerability in xmonad-contrib.
The vulnerability is in the XMonad.Hooks.DynamicLog module. It has been
assigned the name CVE-2013-1436.

Background
==========
DynamicLog module feeds information to others programs about what's
happening on xmonad window manager. Such programs generally are status bars
as xmobar or dzen2. These programs features the ability of receiving
formatted input from stdin, and that's the way used by xmonad to
communicate information such as workspace status, current layout and window
title. So far, so good.

Both bars uses some meta-language to format their input. For example,
xmobar will make the following text clickable.

  <action=xclock>Click to clock</action>

Vulnerability & exploit
=======================
As we know, web browsers usually set the window title to the current tab. A
malicious user, then, can craft a special title in order to inject commands
in the current bar. In xmobar this will be something like this:

<html>
        <head>
                <title>&lt;action=xclock&gt;An innocent title&lt;/action&gt;</title>
        </head>
        <body>
                <h1>Good bye, cruel world</h1>
        </body>
</html>

So, if the user accidentally (or incidentally) clicks on the xmobar window
title, the command will be executed. In dzen2 this is also possible,
although I haven't tried to execute code. A (harmless) proof of concept is
attached for both bars. The proof for dzen2 just changes the background
color of the bar.

Fix
===
A fix for this issue is already available in xmonad webpage[0]. A patch
written by Adam Vogt can be retrieved from the commit in the darcs repo[1].
If you use this module, please make sure to recompile your xmonad binary
after upgrading the package.

I would like to thank Joachim Breitner and the Debian Security Team for
their help in disclosing this issue.

Cheers.

[0] http://hackage.haskell.org/packages/archive/xmonad-contrib/0.11.2/xmonad-contrib-0.11.2.tar.gz
[1] http://handra.rampa.sk/dawb/patch?repoPURL=http%3A%2F%2Fcode.haskell.org%2FXMonadContrib&repoPHash=20130708144813-1499c-0c3e284d3523c0694b9423714081761813bc1e89

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