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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.

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Issue:

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.

Mitigating Factors:

• 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.

Risk Rating:

• Internet systems: Low
• Intranet systems: Low
• Client systems: Moderate

Patch Availability:

• A patch is available to fix this vulnerability. Please read the
  Security Bulletin at
  http://www.microsoft.com/technet/security/bulletin/ms02-014.asp
  for information on obtaining this patch.

Acknowledgment:

• • eEye Digital Security (http://www.eeye.com)

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