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Home » Hacking News » Winhlp32.exe Remote BufferOverrun

Winhlp32.exe Remote BufferOverrun

by Nikola Strahija on August 2nd, 2002 Many of the features available in HTML Help are implemented through the HTML Help ActiveX control (HHCtrl.ocx). The HTML Help ActiveX control is used to provide navigation features (such as a table of contents), to display secondary windows and pop-up definitions, and to provide other features. The HTML Help ActiveX control can be used from topics in a compiled Help system as well as from HTML pages displayed in a Web browser.

The functionality provided by the HTML
Help ActiveX control will run in the HTML Help Viewer or in any
browser that supports ActiveX technology, such as Internet Explorer
(version 3.01 or later). Some features, as with the WinHlp Command,
provided by the HTML Help ActiveX control are meant to be available
only when it is used from a compiled HTML Help file (.chm) that is
displayed by using the HTML Help Viewer.


Winhlp32.exe is vulnerable to a bufferoverrun attack using the Item
parameter within WinHlp Command, the item parameter is used to
specify the file path of the WinHelp (.hlp) file in which the WinHelp
topic is stored, and the window name of the target window. Using
this overrun, an attacker can successfully exectute arbitary code on
a remote system by either encouraging the victim to visit a
particular web page, whereby code would execute automatically, or by
including the exploit within the source of an email. In regards to
email, execution would automatically occur when the mail appears in
the preview pane and ActiveX objects are allowed (This is allowed by
default, the Internet Security Settings would have to be set as HIGH
to prevent execution of this vulnerability). Any exploit would
execute in the context of the logged on user.

Visual POC Exploit

This POC will simply display Calculator. Please note that this
written on a Win2k PC with SP2 installed. I have not tested it on
anything else.


Fix Information

NGSSoftware alerted Microsoft to these problems on the 6th March
2002. NGSSoftware highly recommend installing Microsoft Windows SP3,
as the fix has been built into this service pack found at
An alternative to these patches would be to ensure the security
settings found in the Internet Options is set to high. Despite the
Medium setting, stating that unsigned ActiveX controls will not be
downloaded, Kylie will still execute Calc.exe. Another alternative
would be to remove winhlp32.exe if it is not required within your
A check for these issues has been added to Typhon II, of which more
information is available from the
NGSSoftware website,

Further Information

For further information about the scope and effects of buffer
overflows, please see

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