Update 08.05.2009 - CHANGES to original advisory [TZO-172009] Trendmicro :

Status : RAR / CAB issue WILL be patched on June 17

Quoting vendor :
"This vulnerability is capable of allowing attackers to send RAR / CAB with corrupted RAR headers through our gateway products, which bypass the compressed files without scanning them."

This just goes to prove that publishing changes perception, as customers read, react and complain. (Trend previously denied patching). In other words, always publish even if the vendor denies

In the name of all TrendMicro customers I would like to thank those customers that reacted and complained. Without publication there is no change, without those reacting to advisories there is neither.

Proves #2 and #5 at http://blog.zoller.lu/2009/04/dear-thierry-why-are-you-such-arrogant.html
to be valid.

Release mode: Coordinated but limited disclosure.
Ref : TZO-172009 - Trendmicro RAR,CAB,ZIP bypass/evasion
Status : No patch, but mitigation recommendations for certain
products (see below)
BID: http://www.securityfocus.com/bid/34763/references
Vendor : http://www.trendmicro.com/
Security notification reaction rating : Good
Notification to patch time window : n+1 days (no patch)

Disclosure Policy :

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-usersetups 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
  1. 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.
  2. InterScan Messaging Security Appliance
    Impact: Detection is evaded but files are quarantined by default, residual risk of an administrator blocking a file as there is no detection of malicious code.
  3. 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
  4. 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 file will be blocked and the Administrator will receive the email notification.

  5. 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
Quote:"Trend Micro Incorporated is a global leader in network antivirus and Internet content security software and services. Founded in 1988, Trend Micro was a pioneer in secure content and threat management, leading the migration of early virus protection from the desktop to the network server and the Internet gateway. Today, the company continues to advance its comprehensive approach to management of content security threats into the Internet cloud, encompassing information flow beyond the boundaries of the network. With its 24x7 global support operations and dedication to innovative technologies and methodologies, Trend Micro is well positioned to protect its customers against an expanding range of threats that silently endanger business operations, personal information, and property."

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 :

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


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