Kaspersky Web Scanner ActiveX Format String Vulnerability

iDefense Security Advisory 10.10.07
http://labs.idefense.com/intelligence/vulnerabilities/
Oct 10, 2007

I. BACKGROUND

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.

http://www.kaspersky.com/virusscanner/

II. DESCRIPTION

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.

III. ANALYSIS

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.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability within
version 5.0.93.0 of Kaspersky Lab's kavwebscan.dll. Previous versions
are suspected to be vulnerable.

V. WORKAROUND

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.

VI. VENDOR RESPONSE

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.

http://www.kaspersky.com/news?id=207575572

VII. CVE INFORMATION

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.

VIII. DISCLOSURE TIMELINE

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

IX. CREDIT

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

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X. LEGAL NOTICES

Copyright © 2007 iDefense, Inc.

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