Anti-Virus Products Miss Malware in Modified Zip Files

By Larry Seltzer  |  Posted 2004-10-19 Print this article Print

Products from six vendors fail to detect malware when it is contained in a corrupted Zip file.

An anonymous researcher has reported through several sources that anti-virus products from six vendors fail to detect malware when it is contained in a corrupted Zip file. The modification to the Zip file prevents the anti-virus programs from detecting files in it, but it doesnt prevent users from accessing those files, according to an advisory from Internet security research firm iDefense. The vulnerable products are from McAfee Inc., Computer Associates International Inc., Kaspersky Labs, Sophos plc., Eset Software and RAV, according to the advisory.

The problem has to do with the products handling of an error condition in Zip files, which store information about compressed files stored within them in two locations. There is a local header preceding each file in the archive and a global header at the end of the archive. When the uncompressed size of the file within both archives is set to zero, the affected programs fail to detect malware in the files.

According to their advisory, iDefense notified the affected vendors of the problem on September 16. Some responded in time for Mondays advisory. McAfee provided a detailed explanation, fixes for their products, and noted that there are no known exploits of this technique. Computer Associates and Eset also responded and provided fixes, according to iDefense.

Kaspersky indicated that the problem would be fixed in their next release. Neither RAV nor Sophos responded, according to iDefense.

Check out eWEEK.coms Security Center for the latest security news, reviews and analysis. And for insights on security coverage around the Web, take a look at Security Center Editor Larry Seltzers Weblog.

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Larry Seltzer has been writing software for and English about computers ever since—,much to his own amazement—,he graduated from the University of Pennsylvania in 1983.

He was one of the authors of NPL and NPL-R, fourth-generation languages for microcomputers by the now-defunct DeskTop Software Corporation. (Larry is sad to find absolutely no hits on any of these +products on Google.) His work at Desktop Software included programming the UCSD p-System, a virtual machine-based operating system with portable binaries that pre-dated Java by more than 10 years.

For several years, he wrote corporate software for Mathematica Policy Research (they're still in business!) and Chase Econometrics (not so lucky) before being forcibly thrown into the consulting market. He bummed around the Philadelphia consulting and contract-programming scenes for a year or two before taking a job at NSTL (National Software Testing Labs) developing product tests and managing contract testing for the computer industry, governments and publication.

In 1991 Larry moved to Massachusetts to become Technical Director of PC Week Labs (now eWeek Labs). He moved within Ziff Davis to New York in 1994 to run testing at Windows Sources. In 1995, he became Technical Director for Internet product testing at PC Magazine and stayed there till 1998.

Since then, he has been writing for numerous other publications, including Fortune Small Business, Windows 2000 Magazine (now Windows and .NET Magazine), ZDNet and Sam Whitmore's Media Survey.

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