[TZO-17-2009]Trendmicro multiple bypass/evasions
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Trendmicro RAR,CAB,ZIP bypass/evasions
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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