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Microsoft Help and Support Center Argument Injection Vulnerability

04.13.04

BACKGROUND

Help and Support Center is a feature of Microsoft Windows that enables
users to download and install software updates, check hardware
compatibility and perform other system related tasks.

DESCRIPTION

Exploitation of an argument injection vulnerability in the Help and
Support Center feature of Microsoft Corp.'s Windows operating system
allows remote attackers to execute arbitrary code.

HCP URIs are handled via the following command as defined in the
registry key HKLMSOFTWAREClassesHCPshellopencommand:

"C:WINDOWSPCHealthHelpCtrBinariesHelpCtr.exe" -FromHCP -url "%1"

The %1 is replaced by the argument to the HCP:// URI. By embedding
quotes in the argument, it is possible to insert new arguments to the
command. For example:

HCP://" -url "../../unreachable.htm

When the %1 is substituted in, this gives:

C:WINDOWSPCHealthHelpCtrBinariesHelpCtr.exe -FromHP -url "HCP://"
-url "../../unreachable.htm"

An attacker can compromise a vulnerable system by crafting a URL to
inject scripting code into a pre-existing file such as
Systemerrorsconnection.htm. The scripting code executes under the "My
Computer" zone.

ANALYSIS

Successful exploitation allows an attacker to remotely execute arbitrary
code under the context of the My Computer zone. Script code executing
with such privileges can be crafted to retrieve and execute arbitrary
third-party code, thereby leading to further compromise.

DETECTION

iDEFENSE has confirmed the existence of this vulnerability in the latest
versions of Windows Server 2003 and Windows XP.

WORKAROUND

S

As stated in Microsoft advisory MS03-044, the HCP protocol can be
unregistered, thereby preventing successful exploitation. This can be
accomplished by deleting the key 'HKEY_CLASSES_ROOTHCP' using the
windows registry editor.

VENDOR RESPONSE

Microsoft has issued the following update to address this vulnerability:

- Security Update for Microsoft Windows (835732)

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2003-0907 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

CREDIT

Jouko Pynnönen (http://iki.fi/jouko) is credited with this discovery.

Get paid for vulnerability research
http://www.idefense.com/poi/teams/vcp.jsp

LEGAL NOTICES

Copyright © 2004 Verisign, 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.