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Kaspersky Web Scanner ActiveX Format String Vulnerability



Kaspersky Lab Online Virus Scanner is a free online virus scanner service, enabling a user to scan their system for malicious code via their Web browser. This online service can be accessed at following URL.



Remote exploitation of a format string vulnerability in Kaspersky Lab's Online Scanner virus scanner service could allow an attacker to execute arbitrary code within the security context of the targeted user.

This vulnerability specifically exists in the Kaspersky online virus scanner ActiveX control. The ActiveX control in question has the following identifiers:

 ProgID: kavwebscan.CKAVWebScan ClassID: 0EB0E74A-2A76-4AB3-A7FB-9BD8C29F7F75 File: kavwebscan.dll 

This ActiveX control passes attacker supplied data as the format string parameter of various string formatting functions. This is presumably done to enable displaying localized messages from within the HTML page. By rendering a specially crafted web page using this ActiveX control, a heap based buffer overflow could occur.


Exploitation of this vulnerability would allow a remote attacker to execute arbitrary code within the context of the targeted user. To exploit this vulnerability, an attacker would need to persuade the victim into viewing a malicious website.

This ActiveX control is installed during the use of the Kaspersky Online Virus Scanner. Once the vulnerable ActiveX control is installed, it will remain installed until they explicitly remove it. If the user doesn't have Kaspersky Online Scanner Control installed, the exploit page could prompt the user to install this ActiveX.

Though this is a format string vulnerability, the traditional "%n" technique will not work. This is due to this ActiveX being compiled with Microsoft Visual Studio 2005, in which the "%n" format specifier is disabled by default. However, the attacker could still exploit the vulnerability using other methods.


iDefense has confirmed the existence of this vulnerability within version of Kaspersky Lab's kavwebscan.dll. Previous versions are suspected to be vulnerable.


Setting the kill-bit for this control will prevent it from being loaded within Internet Explorer. However, doing so will also prevent legitimate use of the control.


Kaspersky Lab has addressed this vulnerability by publishing a new version of the vulnerable ActiveX control. For more information, consult Kaspersky's press release at the following URL.



The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2007-3675 to this issue. This is a candidate for inclusion in the CVE list (http://cve.mitre.org/), which standardizes names for security problems.


06/20/2007 Initial vendor notification
06/21/2007 Initial vendor response
10/10/2007 Coordinated public disclosure


This vulnerability was reported to iDefense by Stephen Fewer of Harmony Security (www.harmonysecurity.com).

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Copyright © 2007 Verisign, Inc.

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