Public Vulnerability Reports

Kaspersky AntiVirus UPX File Decompression DoS Vulnerability



Kaspersky Antivirus is a popular client and gateway virus scanner for Unix and Windows. UPX, the ultimate packer for executables, is a method for compressing executable files to reduce their size on disk. For more information, visit the vendor's site at the following URL.


Remote exploitation of a denial of service (DoS) vulnerability in Kaspersky Lab's Antivirus could allow an attacker to conduct a DoS attack on a targeted host.

The antivirus engine is vulnerable to a DoS condition when processing an executable packed with UPX compression. Malformed compressed data causes the decompression routine to enter an infinite loop. Specifically, a negative data offset results in the same compressed data chunk being processed endlessly.


Exploitation allows an attacker to conduct a DoS attack.

If this attack is conducted against an e-mail gateway running Kaspersky, legitimate clients may be unable to send e-mail through the server.

The infinite loop being executed consists of a short sequence of instructions, which results in maximum CPU usage. On a client desktop, the infinite loop will render the machine nearly unusable. On a server, it severely degrades the quality of service of other applications running.


iDefense has confirmed the existence of this vulnerability in Kaspersky Labs Antivirus Engine version for Windows and 5.5-10 for Linux. Previous versions may also be affected. Any products that use the scanning engine are also affected, which includes the Kaspersky e-mail gateway scanner.


iDefense is currently unaware of any workarounds for this issue.


Kaspersky Lab reports that it has fixed this vulnerability as of February 7th, 2007. In addition, they stated the following.

"There is no need to download any special patches. All installed Kaspersky Lab products are updated automatically through the regular signature-update functionality. There is not need to contact Kaspersky Lab to obtain this fix."


A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not been assigned yet.


01/24/2007 Initial vendor notification
03/01/2007 Initial vendor response
03/02/2007 Coordinated public disclosure


The discoverer of this vulnerability wishes to remain anonymous.

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Copyright © 2007 Verisign, Inc.

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