Title: Unchecked Buffer in Windows Shell Could Lead to Code Execution Date: 07 March 2002 Software: Microsoft Windows 98, NT 4.0, 2000 Impact: Run code of attacker's choice Max Risk: Moderate Bulletin: MS02-014
Microsoft encourages customers to review the Security Bulletin at: http://www.microsoft.com/technet/security/bulletin/MS02-014.asp.
The Windows Shell is responsible for providing the basic framework of the Windows user interface experience. It is most familiar to users as the Windows Desktop, but also provides a variety of other functions to help define the user's computing session, including organizing files and folders, and providing the means to start applications.
An unchecked buffer exists in one of the functions that helps to locate incompletely removed applications on the system. A security vulnerability results because it is possible for a malicious user to mount a buffer overrun attack and attempt to exploit this flaw. A successful attack would have the affect of either causing the Windows Shell to crash, or causing code to run in the user's context.
Be default, this is not remotely exploitable. However, under very unusual conditions, it could be exploited via a web page - - specifically, if the user has installed an application with custom URL handlers and then uninstalled that application, and the uninstall failed to correctly remove the application completely. An attacker could then attempt to levy an attack by constructing an HTML web page that seeks to exploit the vulnerability, and then posting it on their web site or sending it by email.
In a default installation, this vulnerability is not remotely exploitable and could only be exploited by introducing hostile code to the system.
The vulnerability can be remotely exploited only on machines that have installed and uninstalled software which implements customer URL handlers and the software's uninstall failed to completely remove the application from the system.
Outlook 98 and 2000 (after installing the Outlook Email Security Update), Outlook 2002, and Outlook Express 6 all open HTML mail in the Restricted Sites Zone. As a result, customers using these products would not be at risk from email-borne attacks.
The buffer overrun would allow code to run in the security context of the user rather than the system. The specific privileges the attacker could gain through this vulnerability would therefore depend on the privileges accorded to the user.
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