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Microsoft's Malformed E-Mail Header Vulnerability
Microsoft's Malformed E-Mail Header Vulnerability Privacy and Legal Notice


K-060: Microsoft's Malformed E-Mail Header Vulnerability

July 19, 2000 23:00 GMT
PROBLEM:       Microsoft has identified a buffer overflow vulnerability that
               occurs when downloading e-mail. The buffer overflow can occur
               even if the user does not open or preview the e-mail message.
PLATFORM:      Platforms running the following versions may be vulnerable:
                 Microsoft Outlook Express 4.0, 4.01, 5.0, 5.01.
                 Microsoft Outlook 97, 98, 2000.
DAMAGE:        A malicious user can cause the system reading the e-mail to
               crash or to run arbitrary code.
SOLUTION:      Upgrade the software as directed below.

VULNERABILITY The risk is HIGH. The problem and exploits have been presented ASSESSMENT: in public forums.
[ Start Microsoft Advisory ] Microsoft Security Bulletin (MS00-043) Patch Available for "Malformed E-mail Header" Vulnerability Originally posted: July 18, 2000 Summary Microsoft has released a patch that eliminates a security vulnerability in Microsoft (r) Outlook (r) and Outlook Express. Under certain conditions, the vulnerability could allow a malicious user to cause code of his choice to execute on another user's computer. Frequently asked questions regarding this vulnerability and the patch can be found at Issue A component shared by Outlook and Outlook Express contains an unchecked buffer in the functionality that parses e-mail headers when downloading mail via either POP3 or IMAP4. By sending an e-mail that overruns the buffer, a malicious user could cause either of two effects to occur when the mail was downloaded from the server by an affected e-mail client: If the affected field were filled with random data, the e-mail could be made to crash. If the affected field were filled with carefully-crafted data, the e-mail client could be made to run code of the malicious user's choice. Customers who have installed Internet Explorer 5.01 Service Pack 1, and customers who have installed Internet Explorer 5.5 on any system other than Windows 2000, would not be affected by this vulnerability. Likewise, Outlook users who have configured Outlook to use only MAPI services would not be affected, regardless of what version of Internet Explorer they have installed. Affected Software Versions Microsoft Outlook Express 4.0 Microsoft Outlook Express 4.01 Microsoft Outlook Express 5.0 Microsoft Outlook Express 5.01 Microsoft Outlook 97 Microsoft Outlook 98 Microsoft Outlook 2000 Patch Availability The vulnerability can be eliminated by a default installation of either of the following upgrades: Internet Explorer 5.01 Service Pack 1. Internet Explorer 5.5 on any system except Windows 2000. Note: A non-default installation of IE 5.01 SP1 or IE 5.5 also will eliminate this vulnerability, as long as an installation method is chosen that installs upgraded Outlook Express components. Note: When installed on a Windows 2000 machine, IE 5.5 does not install upgraded Outlook Express components, and therefore does not eliminate the vulnerability. However, Windows 2000 Service Pack 1 will install IE 5.5 and upgrade the Outlook Express components at the same time. Note: Patches will be available shortly that will eliminate the vulnerability without requiring a full version upgrade. When they are available, we will update this bulletin and re-release it. Note Additional security patches are available at the Microsoft Download Center More Information Please see the following references for more information related to this issue. Frequently Asked Questions: Microsoft Security Bulletin MS00-043, Microsoft Knowledge Base article Q267884 discusses this issue and will be available soon. Microsoft TechNet Security web site, Obtaining Support on this Issue This is a fully supported patch. Information on contacting Microsoft Technical Support is available at Acknowledgments Microsoft thanks USSR Labs ( for reporting this issue to us and working with us to protect customers Revisions July 18, 2000: Bulletin Created. THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Last Updated July 18,2000 (c) 2000 Microsoft Corporation. All rights reserved. Terms of use. [ End Microsoft Advisory ]

CIAC wishes to acknowledge the contributions of Microsoft for the information contained in this bulletin.
CIAC services are available to DOE, DOE Contractors, and the NIH. CIAC can be contacted at:
    Voice:          +1 925-422-8193 (7 x 24)
    FAX:            +1 925-423-8002
    STU-III:        +1 925-423-2604
    World Wide Web:
                     (same machine -- either one will work)
    Anonymous FTP:
                     (same machine -- either one will work)

This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes.
[Privacy and Legal Notice]

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