WEBsweeper/MIMEsweeper Executable File Content Check bypass Vulnerability 


Digital Armaments advisory is 12.15.2005
http://www.digitalarmaments.com/2005161283546323.html

I. Background

WEBsweeeper/MIMEsweeper is a commercial software that brings policy-based content security to the HTTP gateway. For many information or detail about the software you can refer to the vendor's homepage:

http://www.mailsweeper.com/

II. Problem Description

An attacker could trick a user to click on a mail link/attachment to download and run a malicious code (any malicious application in a .exe file). The ".exe" files should be filtered according to the security policies, but an attacker can trick to fail this test if the data sent to the webserver does not include the ".exe" extension. This problem persist on all platform where the data sent to a webserver (GET or POST) is fetched via a server side language (asp, php, etc..) that doesn't explicitly contain those regular expression. An example is:

http://yourattack.server/asp?cmd=data&maliciouscodewithnumber&number=123

III. Detection

This problem has been detected on latest version of WEBsweeper and MIMEsweeper actually avaiable and on prior version. It persist on all platforms.

IV. Impact analisys

Successful exploitation allow an attacker to easily trick a user to execute malicious code on his system. This attack bypass the protection offered by those content filter application. No exploit code is required. This attack can also be use in a massive way versus clients systems.

V. Solution

The vendor has given no response.
First notification 12.15.2005.
Second notification 12.19.2005.

VI. Credit

Oliver Muenchow - o.muenchow@netprotect.ch is credited with this discovery.

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