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[BMSA-2009-02] XML injection in PyBlosxom
From: Nam Nguyen <namn () bluemoon com vn>
Date: Mon, 9 Feb 2009 09:34:02 +0700

BLUE MOON SECURITY ADVISORY 2009-02
===================================


:Title: XML Injection in PyBlosxom
:Severity: Low
:Reporter: Blue Moon Consulting
:Products: PyBlosxom v1.4.3
:Fixed in: --


Description
-----------

PyBlosxom is a lightweight file-based weblog system. The project started as a Python clone of Blosxom but has since 
evolved into a beast of its own. PyBlosxom focuses on three things: simplicity, extensibility, and community.

In v1.4.3, PyBlosxom suffers an XML injection issue. This allows a malicious user to insert abitrary code into the XML 
output from PyBlosxom.

The problem is with Atom flavor. Its ``head.atom`` uses ``$(url)`` and ``$url`` variables, in many places, that were 
not properly escaped. Injection can be made by forcing PyBloxsom to use Atom flavor such as 
``http://host/path/%3Ccool%3E?flav=atom``. A tag ``<cool>`` is injected in such URL.

Blue Moon Consulting has verified the bug in version 1.4.3. It is highly likely that it also exists in older versions 
starting from 1.3.

Workaround
----------

Disable Atom flavor by deleting ``atom.flav`` directory.

Fix
---

Users of PyBlosxom are advised to contact the vendor directly for a proper fix.

Disclosure
----------

Blue Moon Consulting adapts `RFPolicy v2.0 <http://www.wiretrip.net/rfp/policy.html>`_ in notifying vendors.

:Initial vendor contact:

  February 07, 2009: Initial contact sent to Will Guaraldi.

:Vendor response:

  February 07, 2009: Will replied PyBlosxom did not use XML, so there could be no XML injection bug.

:Further communication:

  February 07, 2009: Replied to Will that we did find such bug.

  February 08, 2009: Will was skeptical about the bug but asked us to file it in the bug tracker anyway.

  February 08, 2009: We replied that filing security bug in a public bug tracker was not our disclosure practice. We 
again stated our disclosure policy and asked Will to accept it before we could send him further details.

  February 08, 2009: Will said he would not make any agreement. We therefore decided to alert the public. 

:Public disclosure: February 09, 2009

:Exploit code: No exploit code is needed.

Disclaimer
----------

The information provided in this advisory is provided "as is" without warranty of any kind. Blue Moon Consulting Co., 
Ltd disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a 
particular purpose. Your use of the information on the advisory or materials linked from the advisory is at your own 
risk. Blue Moon Consulting Co., Ltd reserves the right to change or update this notice at any time.

Attachment: _bin
Description:

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