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Title: Java Applet Can Redirect Browser Traffic
Date: 04 March 2002
Software: Microsoft Virtual Machine
Impact: Information Disclosure
Max Risk: Critical
Bulletin: MS02-013

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS02-013.asp.

---

Issue:

The Microsoft VM is a virtual machine for the Win32 operating
environment. It runs atop Microsoft Windows 95, Microsoft
Windows 98, ME, Windows NT 4.0 , Windows 2000 and Windows XP.
It ships as part of Windows 98, ME, and Windows 2000 and also as
part of Internet Explorer 5.5 and earlier.

The version of the Microsoft VM that ships with Internet Explorer
version 4.x and 5.x contains a flaw affecting how Java requests
for proxy resources are handled. A malicious Java applet could
exploit this flaw to re-direct web traffic once it has left
the proxy server to a destination of the attacker's choice.

An attacker could use this flaw to send a user's Internet session
to a system of his own control, without the user being aware of
this. The attacker could then forward the information on to the
intended destination, giving the appearance that the session was
behaving normally. The attacker could then send his own malicious
response, making it seem to come from the intended destination,
or could discard the session information, creating the impression
of a denial of service. Additionally, the attacker could capture
and save the user's session information. This could enable him
to execute a replay attack or to search for sensitive information
such as user names or passwords.

A system is only vulnerable if IE is used in conjunction with a
proxy server. Users whose browsers are not behind a proxy server
are not vulnerable to this vulnerability. However, those users
would be vulnerable if they changed their browser to use a proxy
server at a later date.

Mitigating Factors:

• The vulnerability only affects configurations that utilize a
  proxy server. Customers who are not using a proxy server are
  not at risk from this vulnerability.

• Best practices strongly recommend using SSL to encrypt sensitive
  information such as user names, passwords and credit card numbers.
  If this has been done, sensitive information will be protected
  from examination and disclosure by an attacker exploiting this
  vulnerability.

Risk Rating:

• Internet systems: Moderate
• Intranet systems: Moderate
• Client systems: Critical

Patch Availability:

• A patch is available to fix this vulnerability. Please read the
  Security Bulletin at
  http://www.microsoft.com/technet/security/bulletin/ms02-013.asp
  for information on obtaining this patch.

Acknowledgment:

• Harmen van der Wal (http://www.xs4all.nl/~harmwal/)

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