Public Vulnerability Reports

Microsoft Help and Support Center Argument Injection Vulnerability



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.


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.


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.


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



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.


Microsoft has issued the following update to address this vulnerability:

- Security Update for Microsoft Windows (835732)


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 (, which standardizes names for
security problems.


Jouko Pynnönen ( is credited with this discovery.

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Copyright © 2004 Verisign, Inc.

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