iDEFENSE Security Advisory 03.09.04: Microsoft Outlook "mailto:" Parameter Passing Vulnerability

Microsoft Outlook "mailto:" Parameter Passing Vulnerability

iDEFENSE Security Advisory 03.09.04
www.idefense.com/application/poi/display?id=79&type=vulnerabilities
March 09, 2004

I. BACKGROUND

Microsoft Outlook provides an integrated solution for managing and
organizing e-mail messages, schedules, tasks, notes, contacts, and other
information. More information is available at
http://www.microsoft.com/outlook/.

II. DESCRIPTION

Insufficient filtering of parameters passed to Microsoft Corp.'s Outlook
e-mail client via the "mailto:" URI (RFC 2368) allows for remote script
execution within the "Local Machine" zone. When Outlook is installed, it
is enabled as the default e-mail handler. A "mailto:" URI will spawn
Outlook with the following command line switches:

OUTLOOK.EXE -c IPM.Note /m "...

The problem manifests when the string '"' is interspersed within
the URI, thereby allowing an attacker to manipulate the command line
switches that Outlook is instantiated with. The following example URI:

... mailto:aa" /profile "xx" ...

causes Internet Explorer to start Outlook as such:

OUTLOOK.EXE -c IPM.Note /m "aa" /profile "xx"

If the "Outlook Today" view is the starting view, an attacker can
manipulate Outlook to start with a specified URL. In a default
installation, this is the case. The URL can be of the form
'javascript:…', allowing an attacker to execute arbitrary script code.
In some implementations, this script code executes under the context of
the "Local Machine" zone. An attacker does not need to socially engineer
a target user into clicking on a malicious link, as the process can be
started automatically by embedding the "mailto:" URI within an HTML
<IMG> tag.

III. ANALYSIS

Successful exploitation allows an attacker to remotely execute arbitrary
code under the context of the "Local Machine" zone. Script code
executing with such privileges can be crafted to retrieve and execute
arbitrary third-party code, thereby leading to further compromise.

iDEFENSE has proof of concept exploit code demonstrating the impact of
this vulnerability.

IV. DETECTION

iDEFENSE has confirmed the existence of this vulnerability in Microsoft
Outlook 2002.

V. WORKAROUND

Microsoft recommends the following workaround strategies:

• Do not use "Outlook Today" as the default home page in Outlook 2002.

• If you are using Outlook 2002 or Outlook Express 6.0 SP1 or later,
  read e-mail messages in plain text format to help protect yourself from
  the HTML e-mail attack vector.

Specific details for implementing these workarounds can be found in
Microsoft advisory MS04-009
(http://www.microsoft.com/technet/security/Bulletin/MS04-009.mspx&#41;.

The Microsoft advisory states that "the 'Outlook Today' home page is
only the default folder home page when an Outlook profile is originally
configured without any e-mail accounts". Our testing has shown that
default view is only changed from "Outlook Today" to "Inbox" when email
accounts are added via the wizard that appears when Outlook is first
launched. The default view does not change when email accounts are added
via either the "Tools…E-Mail Accounts" menu within Outlook or
"Start…Control Panel…Mail…E-Mail Accounts". This remains true for
Outlook 2002 SP3.

VI. VENDOR RESPONSE/FIX

Microsoft has released the following patches to address this issue:

Microsoft Office XP Service Pack 2
http://www.microsoft.com/downloads/details.aspx?FamilyId=52F1A951-24DB-4
4A5-9475-EA5D302BCA6A&displaylang=en

Microsoft Outlook 2002 Service Pack 2
http://www.microsoft.com/downloads/details.aspx?FamilyId=52F1A951-24DB-4
4A5-9475-EA5D302BCA6A&displaylang=en

VII. CVE INFORMATION

The Mitre Corp.'s Common Vulnerabilities and Exposures (CVE) Project
has assigned CAN-2004-0121 to this issue.

VIII. DISCLOSURE TIMELINE

October 10, 2003 Vulnerability acquired by iDEFENSE
November 12, 2003 Initial vendor notification
November 12, 2003 Initial vendor response
November 21, 2003 iDEFENSE clients notified
March 09, 2004 Coordinated public disclosure

IX. CREDIT

Jouko Pynnönen (http://iki.fi/jouko&#41; is credited with this discovery.