[Esa-l] ADVISORY: MSN Messenger OCX Buffer Overflow (fwd)

John D. Hardin jhardin at impsec.org
Wed May 8 18:26:00 PDT 2002

One good reason not to set SECURITY_TRUST_HTML...

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---------- Forwarded message ----------
Date: Wed, 8 May 2002 16:00:03 -0700
From: Marc Maiffret <marc at eeye.com>
To: BUGTRAQ <BUGTRAQ at securityfocus.com>
Subject: ADVISORY: MSN Messenger OCX Buffer Overflow

MSN Messenger OCX Buffer Overflow

Release Date:

High (Remote code execution)

Systems Affected:
Microsoft MSN Chat Control
Microsoft MSN Messenger 4.5 and 4.6, which includes the MSN Chat control
Microsoft Exchange Instant Messenger 4.5 and 4.6, which includes the MSN
Chat control

A vulnerability has been discovered in the parameter handling of the MSN
Messenger OCX. By exploiting this vulnerability, an attacker can supply and
execute code on any machine on which MSN Messenger with the activex is

The vulnerability exists because of how MSN Messenger handles data passed to
it which can lead to a buffer overflow scenario. The buffer overflow can be
exploited via email, web, or through any other method where Internet
Explorer is used to display HTML that an attacker supplies, including
software that uses the web browser ActiveX control.

All users of Internet Explorer are potentially affected because this is a
Microsoft signed OCX. Users that have not installed Microsoft Messenger or
that have not upgraded Microsoft Messenger can only be affected if they
accept the pop-up "Install Now" signed by Microsoft. All Internet Explorer
users should install the update.


<DEFANGED_object classid="clsid:9088E688-063A-4806-A3DB-6522712FC061" width="455"
<param name="_cx" value="12039">
<param name="_cy" value="13838">
<param name="BackColor" value="50331647">
<param name="ForeColor" value="43594547">
<param name="RedirectURL" value="">
<param name="ResDLL" value="AAAAAAA[27,257 bytes is where the EIP starts]">

Technical Description:

MSNChat ocx is an ActiveX object installed with Microsoft Messenger. Proper
bounds checking is not in place in the ResDLL parameter. By supplying a very
large buffer, we can overwrite a significant portion of the stack, including
saved return addresses and exception handlers.

Even if users do not have Messenger installed, the ActiveX can be called
from the codebase tag which would prompt the user to install the ActiveX
with Microsoft's credentials because the OCX is signed by Microsoft.

Vulnerability identifier: CAN-2002-0155

Vendor Status:
Microsoft has released a security bulletin and patch. For more information

Discovery: Drew Copley

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