ID

VAR-200501-0310

CVE

CVE-2004-0934

TITLE

Anti-virus software may not properly scan malformed zip archives

DESCRIPTION

Kaspersky 3.x to 4.x allows remote attackers to bypass antivirus protection via a compressed file with both local and global headers set to zero, which does not prevent the compressed file from being opened on a target system. Anti-virus software may rely on corrupted headers to determine if a zip archive is valid. As a result, anti-virus software may fail to detect malicious content within a zip archive. Multiple Vendor Antivirus applications are reported vulnerable to a zip file detection evasion vulnerability. This vulnerability may allow maliciously crafted zip files to avoid being scanned and detected. The malicious archive can bypass the protection provided by a vulnerable antivirus program, giving users a false sense of security. If the user opens and executes the file, this attack can result in a malicious code infection. This issue is reported to affected products offered by McAfee, Computer Associates, Kaspersky, Sophos, Eset and RAV. Latest antivirus products by Symantec, Bitdefender, Trend Micro and Panda are not vulnerable to this issue. Kaspersky is a well-known antivirus software. Kaspersky 3.x and 4.x versions have issues when processing .zip files, resulting in a vulnerability to bypass antivirus checks. II. DESCRIPTION Remote exploitation of an exceptional condition error in multiple vendors' anti-virus software allows attackers to bypass security protections by evading virus detection. The .zip file format stores information about compressed files in two locations - a local header and a global header. The local header exists just before the compressed data of each file, and the global header exists at the end of the .zip archive. It is possible to modify the uncompressed size of archived files in both the local and global header without affecting functionality. This has been confirmed with both WinZip and Microsoft Compressed Folders. An attacker can compress a malicious payload and evade detection by some anti-virus software by modifying the uncompressed size within the local and global headers to zero. III. ANALYSIS Successful exploitation allows remote attackers to pass malicious payloads within a compressed archive to a target without being detected. Most anti-virus engines have the ability to scan content packaged with compressed archives. As such, users with up-to-date anti-virus software are more likely to open attachments and files if they are under the false impression that the archive was already scanned and found to not contain a virus. IV. The Vendor Responses section of this advisory contains details on the status of specific vendor fixes for this issue. V. WORKAROUND Filter all compressed file archives (.zip) at border gateways, regardless of content. VI. VENDOR RESPONSES McAfee "The McAfee scan engine has always been a market leader in detection of viruses, worms and Trojans within compressed and archived file formats. As such the mechanism used for the detection of such payloads has been designed to ensure all archive files are thoroughly scanned at each nested level in the file to ensure that all appropriate parts of the file are scanned. McAfee is aware of a proof of concept exploitation in Zip archive payloads where information in the local header part of the archive is modified. The local header exists just before the compressed data of each file. It is possible to modify the uncompressed size of archived files in the local header without affecting functionality. Consequently there is the potential for a malicious payload to be hidden and avoid anti-virus detection by modifying the uncompressed size within the local headers to zero. The techniques used by McAfee to analyze Zip archives have allowed a comprehensive solution for the Zip file format vulnerability to be provided to protect customers. The latest update for the current 4320 McAfee Anti-Virus Engine DATS drivers (Version 4398 released on Oct 13th 2004) further enhances the protection afforded to McAfee customers against such potential exploits. A DATS Driver update issued in Version 4397 (October 6th 2004) provided early protection for the same potential exploit targeted specifically for Gateway and Command line scanning. If a detection of this type of exploit is found it will trigger the message "Found the Exploit-Zip Trojan!" to be displayed. Updates for the DAT files mentioned above can be located at the following links: Home (Retail) Users: http://download.mcafee.com/uk/updates/updates.asp Business (Enterprise) Users: http://www.mcafeesecurity.com/uk/downloads/updates/dat.asp?id=1 It should be noted that whilst McAfee take the potential for this exploit to be used maliciously seriously, to date no evidence of such an exploit has been discovered. McAfee has provided additional protection through the DATS driver update however with usage of the comprehensive suite of anti-virus protection strategies provided by McAfee products, MacAfee are confident that this exploit presented no additional threat to its customers. It should be noted that with McAfee on-access scanning active, such modification for malicious purposes to hide payloads only delays eventual detection - McAfee on-access detection will detect any payload with malicious intent as malware. McAfee continues to focus on ensuring that customers receive maximum protection and provide a rapid response to all potential vulnerabilities thus ensuring customer satisfaction." Computer Associates "With the assistance of iDEFENSE, Computer Associates has identified a medium-risk vulnerability in a shared component of eTrust Antivirus which may allow a specially crafted .ZIP file to bypass virus detection. A number of CA products embed this technology including solutions from eTrust, Brightstor and others. Customers are encouraged to visit the CA support web site below for more information about this vulnerability, a list of products and platforms that are effected, and remediation procedures. http://supportconnectw.ca.com/public/ca_common_docs/arclib_vuln.asp. At Computer Associates, every reported exposure is handled with the utmost urgency. We strive to ensure that no customer is left in a vulnerable situation." Kaspersky (09/24/2004) "...this bug for scanners based on 3.x-4.x engines will be fixed in next (not current) cumulative update. For scanners based on new 5.0 engine we recommend you waiting for the release of our next maintenance pack. We are going to release it in October." Sophos "A vulnerability has been discovered in Sophos's handling of Zip archive files, whereby a Zip file can be deliberately altered to prevent accurate scanning by Sophos anti-virus products of its contents. Although theoretically a risk, Sophos has not seen any examples of malware attempting to employ this vulnerability. Furthermore, The vulnerability does not prevent Sophos's desktop on-access scanner from correctly detecting viruses (and preventing actual infection) which manage to bypass the email gateway software, so the risks of infection are very small. Sophos has enhanced its scan engine to deal with malformed Zip files. Version 3.87.0 of Sophos Anti-Virus on all operating system platforms except Windows 95/98/Me includes this fix and customers will be automatically updated to this version via EM Library from Wednesday 20 October 2004. Additionally, a version of the software will be available for download from the Sophos website from Friday 22 October 2004. Sophos Anti-Virus for Windows 95/98/Me customers will be updated with the fix from version 3.88.0 (available from 24 November 2004). Sophos thanks iDEFENSE for their assistance in identifying this vulnerability." Eset "The vulnerability was caused by the fact that some archive compression/decompression software (including Winzip) incorrectly handles compressed files with deliberately damaged header fields, thus, in-fact, allowing creation of the damaged archive files, that could be automatically repaired on the victims computer without notifying the user. Eset has made appropriate modifications to archive-scanning code to handle such kind of archives immediately after receiving notification from iDEFENSE. These changes are contained in archive-support module version 1.020, released on 16th September 2004 at 21:00 CET. The update was available for all clients with Automatic Virus-Signatures Update set." RAV No vendor response VII. CVE INFORMATION The Common Vulnerabilities and Exposures (CVE) project has assigned the following names to these issues: CAN-2004-0932 - McAfee CAN-2004-0933 - Computer Associates CAN-2004-0934 - Kaspersky CAN-2004-0937 - Sophos CAN-2004-0935 - Eset CAN-2004-0936 - RAV These are candidates for inclusion in the CVE list (http://cve.mitre.org), which standardizes names for security problems. VIII. DISCLOSURE TIMELINE 09/16/2004 Initial vendor notification 09/16/2004 iDEFENSE clients notified 10/18/2004 Coordinated public disclosure IX. CREDIT The discoverer of this vulnerability wishes to remain anonymous. Get paid for vulnerability research http://www.idefense.com/poi/teams/vcp.jsp X. LEGAL NOTICES Copyright © 2004 iDEFENSE, Inc. Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDEFENSE. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please email customerservice@idefense.com for permission. Disclaimer: The information in the advisory is believed to be accurate at the time of publishing based on currently available information. Use of the information constitutes acceptance for use in an AS IS condition. There are no warranties with regard to this information. Neither the author nor the publisher accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information

AFFECTED PRODUCTS

CVSS

PROBLEMTYPE DATA

THREAT TYPE

remote

TYPE

other

EXPLOIT AVAILABILITY

PATCH

EXTERNAL IDS

REFERENCES

CREDITS

iDEFENSE Security Advisory※ labs@idefense.com

SOURCES

LAST UPDATE DATE

2024-08-14T13:51:14.235000+00:00

SOURCES UPDATE DATE

SOURCES RELEASE DATE