Outlook mailto: URL argument injection vulnerability

[Jouko Pynnonen <jouko () iki fi>]

OVERVIEW
========

Microsoft Outlook contains a vulnerability which allows execution of 
arbitrary code when a victim user views a web page or an e-mail message 
created by an attacker.



DETAILS
=======

During Outlook installation, a mailto: URL handler is registered to the 
system. When a mailto: URL is opened, the system starts OUTLOOK.EXE 
with the following arguments:

  OUTLOOK.EXE -c IPM.Note /m "mailto:email@address";

If the URL contains a quote symbol, additional command line arguments
can be injected to OUTLOOK.EXE. The program recognizes several command
line switches. Also a startup URL to be opened by Outlook can be 
supplied on command line. This URL can be a javascript: URL, and if the 
"Outlook today" page is the current view in Outlook, the JavaScript 
code will be executed in the "Local machine" zone. This allows an 
attacker to e.g. download and start a desired EXE program.

A web page or e-mail message exploiting this flaw may contain for 
instance an IMG tag to refer to a mailto: URL. The victim user need not 
click on a link.

If the "Outlook today" view isn't the default view in Outlook, the 
attacker can still carry out the attack by using two mailto: URLs; The 
information in the mitigating factors section of Microsoft's bulletin 
regarding this is inaccurate. The first mailto: URL would start 
OUTLOOK.EXE and cause it to show the "Outlook today" view, and the 
second one would supply the offending JavaScript code. This scenario 
was verified by an exploit.

The issue is not a standard "cross site scripting" vulnerability, but a 
different kind of injection attack. The exploit can inject command line 
switches and arguments to OUTLOOK.EXE because quote symbols in the URL 
aren't escaped or otherwise processed. This can be considered a new 
vulnerability category, and further investigation has shown that 
similar attacks can be carried out against other software which register 
a URL handler.



AFFECTED VERSIONS
=================

According to Microsoft the affected supported versions are Microsoft 
Office XP SP2 and Microsoft Outlook 2002 SP 2. Some earlier versions 
are vulnerable too, but not supported by the vendor.



SOLUTION
========

Microsoft was informed on July 21st, 2003 and has released an update 
to correct the problem. A bulletin describing the update can be seen
at

  http://www.microsoft.com/technet/security/Bulletin/MS04-009.mspx



CREDITS
=======

The vulnerability was discovered and researched by Jouko Pynnönen, 
Finland.




-- 
Jouko Pynnönen          Web: http://iki.fi/jouko/
jouko () iki fi            GSM: +358 41 5504555

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