[TZO-20-2009] AVG ZIP evasion / bypass

[Thierry Zoller <Thierry@xxxxxxxxx>]

________________________________________________________________________

From the low-hanging-fruit-department - AVG generic ZIP bypass / evasion
________________________________________________________________________

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Release mode: Coordinated but limited disclosure.
Ref         : [TZO-20-2009] - AVG generic ZIP bypass / evasion
WWW         : http://blog.zoller.lu/2009/04/avg-zip-evasion-bypass.html
Vendor      : http://www.AVG.com
Status      : Patched (with engine build 8.5 323)
CVE         : none provided
Credit      : t.b.a
OSVDB vendor entry: none [1]
Security notification reaction rating : good
Notification to patch window : +-28 days 

Comment:
Interestingly at AVG, the support department handles the security
notification response, which strangely seemed to work out this time. I guess 
when
procedures and awareness are in place it doesn't matter that much. 
(You loose the "bouncer effect" for irrelevant reports though). I'd recommend
to designate one person to be responsible to security related issues, and 
"train"
the others to forward to that person (even in case of doubt if security or not)
if you choose to have support department handle security notifications.



Disclosure Policy : 
http://blog.zoller.lu/2008/09/notification-and-disclosure-policy.html

Affected products : 
- AVG Anti-Virus Network Edition (prior to engine build 8.5 323)
- AVG Internet Security Netzwerk Edition (prior to engine build 8.5 323)
- AVG Server Edition für Linux/FreeBSD (prior to engine build 8.5 323)
- AVG eMail Server Edition (prior to engine build 8.5 323)
- AVG File Server Edition (prior to engine build 8.5 323)
- AVG Internet Security SBS Edition (prior to engine build 8.5 323)
- AVG Anti-Virus SBS Edition (prior to engine build 8.5 323)
- AVG Anti-Virus plus Firewall (prior to engine build 8.5 323)
- AVG Anti-Virus (prior to engine build 8.5 323)

I. Background
~~~~~~~~~~~~~
Quote: "Founded in 1991, with corporate offices in Europe, the US 
and the UK, AVG is focused on providing home and business computer
users with the most comprehensive and proactive protection against
computer security threats.

With more than 80 million active users around the world, the AVG 
family of security software products is distributed globally through 
resellers and through the Web and supports all major operating 
systems and platforms."


II. Description
~~~~~~~~~~~~~~~
The parsing engine can be bypassed by a specially crafted and formated
ZIP (Filelenght) archive.

III. Impact
~~~~~~~~~~~
A general description of the impact and nature of AV Bypasses/evasions
can be read at : 
http://blog.zoller.lu/2009/04/case-for-av-bypassesevasions.html

The bug results in denying the engine the possibility to inspect
code within RAR and ZIP archives. There is no inspection of the content
at all and hence the impossibility to detect malicious code.


IV. Disclosure timeline
~~~~~~~~~~~~~~~~~~~~~~~~~
DD/MM/YYYY
10/04/2009 : Send proof of concept, description the terms under which 
             I cooperate and the planned disclosure date.
                         
14/04/2009 : AVG acknowledges reproducibility 

14/04/2009 : I inform AVG that this is a security notification not a simple
             bug report.

15/04/2009 : AVG acknowledges through a second channel

15/04/2009 : AVG informs me that the fix has been made and the code is 
             currently being tested prior to being deployed. 

15/04/2009 : Ask second channel AVG contact what versions and products 
                         are affected.                   
                         
                         no reply
                         
07/05/2009 : Ask AVG wether the patches have now been deployed

08/05/2009 : AVG answers that the patches have been deployed

08/05/2009 : Ask AVG what versions have been affected

08/05/2009 : AVG states that "[..]AVG 8.5 build 285 are affected by this 
             issue but the latest release of AVG 8.5 build 323 has 
                         resolved the reported issue.[..]"       
                         
08/05/2009 : Release of this advisory.


[1]
Grisoft (AVG) is encouraged to leave their security contact details at
http://osvdb.org/vendor/1/Grisoft to facilate communication and reduce
lost reports.