[UNIX] DansGuardian Hex Encoding URL Banned Extension Filter Bypass Vulnerability
From: SecuriTeam (support_at_securiteam.com)
Date: 08/01/04
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To: list@securiteam.com Date: 1 Aug 2004 15:53:20 +0200
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DansGuardian Hex Encoding URL Banned Extension Filter Bypass Vulnerability
------------------------------------------------------------------------
SUMMARY
<http://dansguardian.org> DansGuardian is a web Open Source content
filter available for various Unix based operating systems, including
Linux. It filters the actual content of pages based on many methods
including phrase matching, PICS filtering and URL filtering.
DansGuardian allows malicious users to bypass the extension filter rules
when processing URLs which contain an hex encoded filename.
DETAILS
Vulnerable Systems:
* DansGuardian version 2.8 and prior
Immune Systems:
* DansGuardian version 2.8.0.1
DansGuardian employs a content filter that is used to filter out certain
unwanted type of files among other content. Using a hex encoded filename,
a malicious user is able to fool the content filter, thus bypassing it
completely. An example of such a case can be seen below:
http://server/file.%65%78%65 or http://server/file%2eexe
Under some installations, this vulnerability may violate the security
policy, or allow users to inadvertantly access malicious web content.
Patch Availability:
There is already a newer version available which addresses this
vulnerability. Users are encouraged to upgrade to version 2.8.0.1. As a
temporary workaround, the following patch can be used:
--- FOptionContainer.cpp.diff ---
806d805
< url.hexDecode();
---------------------------------
Disclosure Timeline
28/07/2004 Notification to the main developer (author at dansguardian dot
org)
28/07/2004 DansGuardian 2.8.0.1 released
29/07/2004 Public Security Advisory.
ADDITIONAL INFORMATION
The information has been provided by <mailto:ruben@udea.edu.co> Rub n
Molina.
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