w00w00 (http://www.w00w00.org)
Angry Packet Security (http://sec.angrypacket.com)

Vulnerability in Multiple Microsoft Products for Mac OS
HTML format: http://www.w00w00.org/advisories/ms_macos.html
Text format: http://www.w00w00.org/files/advisories/ms_macos.txt

SOFTWARE VERSIONS AFFECTED

Microsft Internet Explorer
Versions affected: 5.1
Platforms affected: Mac OS 8, 9, and X

Microsft Outlook Express
Versions affected: 5.0.2
Platforms affected: all Mac OS

Microsft Entourage
Versions affected: 2001 and X
Platforms affected: all Mac OS

Microsft PowerPoint
Versions affected: 98, 2001, and X
Platforms affected: all Mac OS

Microsft Excel
Versions affected: 2001 and X
Platforms affected: all Mac OS

Microsft Word
Versions affected: 2001
Platforms affected: all Mac OS

PRELUDE

A bug in Internet Explorer for Mac OS X was originally reported to
Microsoft by Josha Bronson of Angry Packet Security on January 4,
2002. 

Due to some internal mishandling at Microsoft, this was brushed off
until w00w00 informed Microsoft of its intention to release the
information on February 17. We originally gave them a deadline of
two weeks until we discovered that this affected Entourage (an
Outlook-like mail client for Mac OS). When Microsoft determined
this affected most of their Office suite on Mac OS, we felt it was
appropriate to give them time to fix it.

DESCRIPTION

There is a vulnerability in multiple Microsoft products on Mac OS.
The problem lies in the handling of a lengthy subdirectory in the
 directive, such as file:///AAAAAA[...] or 
file://A/A/A/A/[...]. The number of subdirectories is trivial as 
long as there is at least one.

IMPLICATIONS

In most cases, the user would need to click on the link to be
attacked. In the case of Entourage or Outlook Express, however,
just opening the email will cause this. This leaves the
potential for a worm. The magnitude depends on how many people
actually use Entourage and Outlook Express for Mac OS. In all
cases, writing shellcode to exploit this problem is simple.
Given that Mac OS X has a Unix interface, existing PowerPC
shellcode that runs /bin/sh will work. No complex shellcode
is needed to bind to a port or download an application off the
web. The /bin/sh shellcode would need to be changed from an
interactive shell to one that will execute a chain of commands.
There are enough commands on Mac OS X by default to allow an
attacker to download and execute an application off of a web
page.  The downloaded application could do any number of
things, such as read off the user's contact list and send the
same email to exploit to all of the user's contacts.

EXPLOIT

The following HTML file will demonstrate the problem. We chose to
use IMG simply because that is instantly loaded, but an
<A HREF=...> could have been used also. It can also be viewed (in
live form) at http://www.w00w00.org/files/advisories/ie_sample.html.
It overwrites the saved link register which is used for a
subroutine's return address on PowerPC. This will allow remote
execution of arbitrary code. The saved link register is overwritten
by the 0x41424344. This vulnerability will allow up to 1313
characters before the saved link register. Pure binary data
(including NUL bytes) can be used by escaping it (i.e., A as %41).
However, using "%41" will count as three characters, rather than
just one. Note: by character I mean unibyte characters.

<html>
<body>
<img src=[1313 characters]%41%42%43%44>
</body>
</html>

PATCHES

For Internet Explorer, a patch is available from 
http://www.apple.com/macosx/upgrade/softwareupdates.html. For
the other products, the patches can be downloaded from
http://www.microsoft.com/mac/download.

CREDIT

w00w00 would like to thank Angry Packet for involving us in their
efforts to get Microsoft to resolve this problem after their 
attempts failed.




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