[TZO-17-2009]Trendmicro multiple bypass/evasions

[Thierry Zoller <Thierry@xxxxxxxxx>]

______________________________________________________________________

               Trendmicro RAR,CAB,ZIP bypass/evasions
______________________________________________________________________

Release mode: Coordinated but limited disclosure.
Ref         : TZO-172009 - Trendmicro RAR,CAB,ZIP bypass/evasion
WWW         : 
http://blog.zoller.lu/2009/04/trendmicro-multiple-evasion-and-bypass.html
Status      : No patch, but mitigation recommendations for certain
              products (see below)
Vendor      : http://www.trendmicro.com/
Security notification reaction rating : Good
Notification to patch time window : n+1 days (no patch)

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

Affected products : 

Client-side products
---------------------
These will not be patched, trends reason is that 
malware will be detected up on extraction. While this is true for end-user
setups this is not the case if you use such products to scan Fileservers, 
Database servers or any server where an enduser does not actively extract 
content. The detection is still completely bypassed. In other words you 
can no longer assume that RAR,ZIP,CAB (or any other archive) is safe/clean 
after 
a Trendmicro scan with these products . 

Hence I can no longer recommend these products for such uses and hence my 
recommendation to trend to offer patches, if you use the products in such
environment please contact Trend and ask for a patch.

I applaud Trend however for the time and effort spent with communicating 
with me and the transparency presented.

Client-side Impact : Low for usage in End-user scenarios
Client-side Impact : High for usage in fileserver, database scenarios.

1. OfficeScan product suites (All of OfficeScan products)
2. ServerProtect product suite (All products of Server protect)
   -ServerProtect for Microsoft Windows/Novell NetWare
   -ServerProtect for EMC Celerra
   -ServerProtect for NetApp
   -Server Protect for Linux
   -ServerProtect for Network Appliance Filers
   
3. Trend Micro Internet Security product suites 
   (Internet Security Pro, Internet Security, Antivirus+AntiSpyware)
4. Client / Server / Messaging Suite ( The OfficeScan component )
5. Worry Free Business Security - Standard 
6. Worry Free Business Security - Advanced ( The security agent component )
7. Worry Free Business Security Hosted 
8. Housecall

Gateway products
-----------------
InterScan Web Security Suite product lines and 
InterScan Web Protect for ISA 
        Impact: Detection is evaded but files are quarantined by default 
        ,residual risk of an administrator deblocking a file as there is 
        no detection of malicious code.
        
InterScan Messaging Security Appliance  
        Impact: Detection is evaded but files are quarantined by default 
        ,residual risk of an administrator deblocking a file as there is 
        no detection of malicious code.
        
Neatsuite Advanced (combination of InterScan Messaging Security Suite,
InterScan Web Security Suite, ScanMail Suite for Domino or Exchange, and All)

   Please see, specific product recommendation

ScanMail for Exchange 
    Impact: Protection is bypassed by default 
    After mitigation: Residual risk of an administrator deblocking a
    file as there is no detection of malicious code.
        
    Mitigation recommendations from Trend:
    1. Set the "Virus Scan > Action > Files outside of scan restriction
       Criteria" to any of the secured options. Quarantined entire message
       and set to Notify
    2. The CAB file will be blocked and the Administrator will
    receive the email notification.
    
ScanMail for Domino Suites
    Impact: Protection is bypassed by default, detection is also bypassed after 
mitigation
    but file is quarantined as "non extractable".
    After mitigation: Residual risk of an administrator deblocking a
    file as there is no detection of malicious code.
    
    Mitigation recommendations from Trend:
    1. Open the ScanMail for Domino Configuration database
    2. Go to Configurations > Policies
    3. Double click on Default Mail Scan
    4. Click on Scan Options Tab > Scan Restrictions
    5. Put a mark on Exceed extracted file size and set this to either of the 
much secured action
        a. Quarantine
        b. Delete
    6. Put any of the preferred value to maximum extracted file size
    7. Click on Save & Closed

                         

I. Background
~~~~~~~~~~~~~
ESET develops software solutions that deliver instant, comprehensive protection 
against evolving computer security threats. ESET NOD32® Antivirus, is the 
flagship
product, consistently achieves the highest accolades in all types of 
comparative testing and is the foundational product that builds 
out the ESET product line to include ESET Smart Security.

http://www.eset.com/products/eset_performance_advantages.php


II. Description
~~~~~~~~~~~~~~~
The parsing engine can be bypassed by a specially crafted and formated
ZIP,RAR,CAB archive. Details are currently witheld due to other vendors 
that are in process of actually deploying patches.

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 the CAB archive. There is no inspection of the content
at all.

Trendmicro decided to no patch the evasion bugs and proposed mitigation
recommendations, the reason given is that doing so would somehow increase
the risk of "buffer overflow and BSOD". I am positive that adding more
code and increase detection rates is probably going to increase your chances
to have such flaws but then again, the goal is to catch as much malware
as possible.

This is fine with me as long as customers exactly know what risk they run 
or don't run when following such recommendations and why other AV vendors
simply reduce the amount of trusted input to a minimum
i.e (only parse and intepret the bare minium required to extract content
of an archive) instead of giving up. In my point of view the goal of an
Anti-virus program is to detect as much malware as possible.


IV. Disclosure timeline
~~~~~~~~~~~~~~~~~~~~~~~~~

14/03/2009 : Send proof of concept, description the terms under which 
             I cooperate and the planned disclosure date
                         
                         No reply
                         
16/03/2009 : Resent
         
                         No reply

09/04/2009 : Resending, specigying this is the last attempt at responsible
             disclosure.

                         No reply
                         
13/04/2009 : Resending, specifying this is the last attempt at responsible
             disclosure (sic)

13/04/2009 : Trend replies and acknowledges receipt of previous reports.

14/04/2009 : Trend replies that 
             "1. Scan Engine found that modified packed size is greater than 
archive 
             size during scanning corrupted RAR.
             2. Scan Engine didn't force to decompress corrupted archive 
because to
             decompress invalid archive could incur unexpected result, for 
example,
             buffer overflow and BSOD.
             [..]
             4. The risk of decompressing invalid archive is much high than 
gateway
             products pass it when get error code -82 (BAD_ZIP_ERR)"
             and
             "virus leak should still not occur because once you decompress the 
archive,
             Real-Time scan will still detect the malware once it's extracted 
out
             of the corrupted archive."
                         
             "One concern that we see from this point is that Gateway products 
won't be
              able to extract the archive during its scanning phase.  (You will 
have
              to manually extract the file for IMSx or IWSx to detect the 
malware).
              However, as stated earlier we cannot force the extraction of 
corrupted
              archives because of other potential issues that could occur.
              So a workaround would be to configure your gateway solution to
              or block files wherein the scan result is "uncertain" or when the
              scan engine returns a specific error code (in this case -82)."
                         
                         
14/04/2009 : Ask trend to reconsider position asuming the files bypass the 
gateway
             appliances.

14/04/2009 : Trend replies with more details clarifying that gateways are 
configured
             to quarantine such files per default.

             14/04/2009 : Ask for clarifications as to product ranges and 
default configurations

14/04/2009 : Trend confirms that the "Gateteway InterScan Messaging 7.0" 
products are 
             configured to quaratine these by default and are investigating on 
the 
             other default configurations.
             "On Trend Micro desktop products, upon testing with the rar and 
the cab
             that you had submitted, the archives will not trigger the scanning
             component. However once the files are extracted by winrar, winzip
             or any other archiving software they will be detected by the Trend
             Micro product before the malicious file can execute."

15/04/2009 : Trendmicro comes back with an detailed list of gateway products and
             default configurations
                         
             Trend recommends 2 mitigation configurations for Scanmail product 
ranges
                         
16/04/2009 : Point out that one of these mitigation configurations opens the 
gateway
             to DoS attacks (allow x times the size of compression archive) and 
ask
             for a list of affected products.

23/04/2009 : Trend changes the mitigation recommendation for one of the 
scanmail products                        

[..] Taking a short cut in the timeline.

29/04/2009 : Release of this advisory