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Microsoft Outlook Express fails to properly validate malformed e-mail headers

Vulnerability Note VU#869640

Original Release Date: 2004-07-14 | Last Revised: 2004-07-23


A vulnerability exists in some versions of Microsoft Outlook Express that could allow a remote attacker to cause a denial of service.


According to Microsoft Security Bulletin MS04-018, a flaw exists in the way that some versions of Microsoft's Outlook Express mail client validate message headers. This flaw results in a vulnerability that could cause the Outlook Express program to crash when an email message containing certain malformed headers are received. The specific nature of the malformation is not known at this time.

Microsoft's bulletin states that the following versions of Outlook Express are affected by this issue:

    • Microsoft Outlook Express 5.5 Service Pack 2
    • Microsoft Outlook Express 6
    • Microsoft Outlook Express 6 Service Pack 1
    • Microsoft Outlook Express 6 Service Pack 1 (64 bit Edition)
    • Microsoft Outlook Express 6 on Windows Server 2003
    • Microsoft Outlook Express 6 on Windows Server 2003 (64 bit edition)


An attacker with the ability to craft and deliver a specially-formed email message could cause the Outlook Express program on the recipient's computer to crash.


Apply a patch from the vendor
Microsoft has released patches to address this issue. Please see the Systems Affected section of this document for more information.


Microsoft lists the following partial workaround for this vulnerability:

Disable the preview pane

Disabling the preview pane will prevent the malicious e-mail message from causing Outlook Express to fail on each restart. To disable the preview pane, follow these steps:

In Outlook Express, click View, and then click Layout.
Click to clear the Show Preview Pane check box, and then click OK.
Note that this workaround will not mitigate the vulnerability, but will prevent the malicious e-mail message from causing Outlook Express to fail on each restart.

Vendor Information

Affected   Unknown   Unaffected

Microsoft Corporation

Updated:  July 14, 2004



Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.


Microsoft Corporation has published Microsoft Security Bulletin MS04-018 in response to this issue. Users are encouraged to review this bulletin and apply the patches it refers to.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

CVSS Metrics

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A



Thanks to Microsoft Security for reporting this vulnerability.

This document was written by Chad R Dougherty based upon information provided in Microsoft Security Bulletin MS04-018

Other Information

CVE IDs: CVE-2004-0215
Severity Metric: 7.48
Date Public: 2004-07-13
Date First Published: 2004-07-14
Date Last Updated: 2004-07-23 18:52 UTC
Document Revision: 16

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