Title: Flaw Could Enable Web Page to Launch Visual FoxPro
6.0 Application Without Warning (Q326568)
Date: 04 September 2002
Software: Microsoft Visual FoxPro 6.0
Impact: Attacker could gain control over user's system.
Max Risk: Moderate
Bulletin: MS02-049

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS02-049.asp.

Issue:

In general, when an product installs, it should register itself with
Internet Explorer. This allows the product to specify how Internet
Explorer should handle files associated with it when referenced from
a web page - for instance, it allows the product to specify whether
the user should be presented with a warning dialogue before such a
file is opened.

Visual FoxPro 6.0 does not perform this registration, and this gives
rise to a situation in which a web page could automatically launch a
Visual FoxPro application (i.e., an .app file). In most cases, this
would not result in a security vulnerability - because of the way
Visual FoxPro 6.0 evaluates file names, FoxPro itself could be
started but the .app file would typically not run. However, if the
filename of the application were constructed in a particular way, a
second error (associated with how Visual FoxPro 6.0 evaluates
application filenames) could not only start FoxPro but allow the
application to execute.

The vulnerability could be exploited by creating a web page that
references a Visual FoxPro application, and either hosting it on a
web site or sending it to a user as an HTML mail. If the user had
installed Visual FoxPro 6.0 - or had installed a product that
includes the Visual FoxPro 6.0 runtime - and the filename of the
application was constructed in a particular way, the application
would execute. This would enable the application to not only
interrogate databases, but also issue system commands in the user's
security context.

Mitigating Factors:

• The vulnerability could only be exploited if Visual FoxPro 6.0
  (or the Visual FoxPro 6.0 runtime) is installed on the system.
  Other products, and other versions of Visual FoxPro, are not
  affected by the vulnerability.
• The most privileges the application could gain would be those
  of the user. If the user were operating in a less-privileged
  context, it would limit the damage that the application could
  cause.

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/ms02-049.asp
  for information on obtaining this patch.

Acknowledgment:

• Cristobal Bielza and Juan Carlos G. Cuartango from Instituto
  Seguridad Internet (http://www.instisec.com)

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