[NT] Finjan SurfinGate Bypass (URL Encoding)

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Finjan SurfinGate Bypass (URL Encoding)
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SUMMARY

The <http://www.finjan.com/> Finjan SurfinGate allows "preforming web
content filtering and Internet access management". A vulnerability in
Finjan SurfinGate product allows attackers to bypass the product's access
management and restriction (You can download files that would be otherwise
blocked).

DETAILS

Vulnerable Systems:
* SurfinGate version 7.0SP2 and SP3

CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-1994>
CAN-2005-1994

An URL ASCII decode problem exists in the Finjan SurfinGate. If an
attacker uses ASCII encoding when trying to access files through the
Finjan SufinGate, the attacker will bypass the security policy enforced by
the product. Due to this flaw, it is possible to bypass EXE download
restriction, or download files that have two or more extensions, for
example file.jpg.exe.

If the product is configured to block specific Content-Type, SurfinGate
will block the download, but an attacker can configure a malicious web
server to return non-blocked Content-Types.

Proof of concept:
Of course we don't take a normal exe-file. Let us use a screensaver. If
you block SCR-files the following will be blocked:
<http://www.mustangworld.com/ourpics/sware/Mustangworld.scr>
http://www.mustangworld.com/ourpics/sware/Mustangworld.scr

If you just block the SCR-extension (and not the content type in your
infrastructure) you can bypass the Finjan SurfinGate by using the
following link:
<http://www.mustangworld.com/ourpics/sware/Mustangworld%2escr>
http://www.mustangworld.com/ourpics/sware/Mustangworld%2escr

Vendor Status:
Finjan Software Ltd. has been notified for a year ago, no response was
received.

ADDITIONAL INFORMATION

The information has been provided by <mailto:d.schroeter@gmx.de> Daniel
Schroter.

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