bugtraq - Unchecked buffer in mstask.dll

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Date: Wed, 14 Jul 2004 17:50:30 +1200
From: "Brett Moore" <brett.moore@...urity-assessment.com>
To: "Bugtraq@...urityfocus. Com" <bugtraq@...urityfocus.com>
Subject: Unchecked buffer in mstask.dll

========================================================================
= Unchecked buffer in mstask.dll
=
= MS Bulletin posted: 
= http://www.microsoft.com/technet/security/bulletin/MS04-022.mspx
=
= Affected Software:
=	Microsoft Windows 2000 Service Pack 4
=	Microsoft Windows XP, Microsoft Windows XP Service Pack 1 
=
= Public disclosure on July 14, 2004
========================================================================

When thinking about buffer overflow vulnerabilities, a file can sometimes
be as harmful as a packet. Even though past security issues have taught
us that it is unwise to use an unvalidated text string containing a file
name or directory, that is what happened here.

By creating a .job file with a large "to be executed" field the stack can
be overwritten allowing for remote command execution, when the file is
parsed by mstask.dll.

== Description ==

It appears that both explorer.exe and iexplore.exe will parse a .job file
when showing folder listings. Upon the parsing of the .job file, the
large "to be executed" field is passed to wcscpy without doing any
bounds checking.

Using explorer the viewing of a folder containing the .job is enough to
cause the buffer overflow to occur. The file can be hosted locally or
on a remote network share. A remote attack would require the end user
to visit the folder/share containing the exploit file.

Using Internet Explorer the viewing of a folder containing the .job file
through the use of an [iframe] object will cause the buffer overflow
to occur.

Viewing an HTML email that is based around the [iframe] attack avenue,
will also cause the buffer overflow. This will occur without any user
intervention if the preview pane is enabled, or with user intervention
by viewing the email.

It is possible that there are other avenues of attack to exploit this
vulnerability. 

== Exploitation ==

Remote exploitation through Internet Explorer can be obtained through the
use of an iframe object pointing at an anonymous share.

Automatic exploitation of browser based bugs, does not rely on an attacker
sending a link, requiring the target user to click on it. Links, references
and other objects can easily be opened through script code. And I am told
that this can also be achieved without script code.

== Solutions ==

- Install the vendor supplied patch.
- Use browser protection products such as Qwik-Fix from PivX. They are to
  implement some protective measure against this very soon.

== Credit ==

Discovered and advised to Microsoft July 7th, 2003 by Brett Moore of
Security-Assessment.com

%-) Thor and the PivX guys, the #unconventional and the #conversational

== About Security-Assessment.com ==

Security-Assessment.com is a leader in intrusion testing and security
code review, and leads the world with SA-ISO, online ISO17799 compliance
management solution. Security-Assessment.com is committed to security
research and development, and its team have previously identified a
number of vulnerabilities in public and private software vendors products.

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