-----BEGIN PGP SIGNED MESSAGE----- CERT Advisory CA-2001-06 Automatic Execution of Embedded MIME Types Original release date: April 03, 2001 Last revised: -- Source: CERT/CC A complete revision history can be found at the end of this file. Systems Affected * All versions of Microsoft Internet Explorer 5.5 SP1 or earlier, except IE 5.01 SP2 * Any software which utilizes vulnerable versions of Internet Explorer to render HTML Overview Microsoft Internet Explorer has a vulnerability triggered when parsing MIME parts in a document that allows a malicious agent to execute arbitrary code. Any user or program that uses vulnerable versions of Internet Explorer to render HTML in a document (for example, when browsing a filesystem, reading email or news messages, or visiting a web page), should immediately upgrade to a non-vulnerable version of Internet Explorer. I. Description There exists in Internet Explorer a table which is used to determine how IE handles MIME types when it encounters MIME parts in any type of HTML document, be it email message, newsgroup posting, web page, or local file. This table contains a set of entries that cause Internet Explorer to open the MIME part without giving the end user the opportunity to decide if the MIME part should be opened. This vulnerability allows an intruder to construct malicious content that, when viewed in Internet Explorer (or any program that uses the IE HTML rendering engine), can execute arbitrary code. It is not necessary to run an attachment; simply viewing the document in a vulnerable program is sufficient to execute arbitrary code. For more details, see Microsoft Security Bulletin MS01-020 on this topic at: http://www.microsoft.com/technet/security/bulletin/MS01-020.asp There have been reports that simply previewing HTML content (as in a mail client or filesystem browser) is sufficient to trigger the vulnerability. The impact of viewing malicious code in this manner is being evaluated. The CERT/CC is currently unaware of any reports of this vulnerability being used to successfully attack a system. Demonstration code exploiting this vulnerability has been published in several public forums. This vulnerability is being referenced in CVE as CAN-2001-0154 and by the CERT/CC as VU#980499. II. Impact Attackers can cause arbitrary code to be executed on a victim's system by embedding the code in a malicious email, or news message, or web page. III. Solution Apply the patch from Microsoft Apply the patch from Microsoft, available at: http://www.microsoft.com/windows/ie/download/critical/Q290108/default.asp As noted in the 'Caveats' section of the Microsoft advisory, end users must apply this patch to supported versions of Microsoft's browser. This means IE must be upgraded to IE 5.01 Service Pack 1 or IE 5.5 Service Pack 1 before users can apply this patch. Users who have not previously upgraded will incorrectly receive a message stating that they do not need to apply this patch, even though they are vulnerable. Users are advised to upgrade to IE 5.5 SP1, IE 5.01 SP1 or SP2 (which has this patch incorporated in it) and apply the appropriate patch. An excerpt from MS01-020: Caveats: If the patch is installed on a system running a version of IE other than the one it is designed for, an error message will be displayed saying that the patch is not needed. This message is incorrect, and customers who see this message should upgrade to a supported version of IE and re-install the patches. Appendix A. - Vendor Information This appendix contains information provided by vendors for this advisory. When vendors report new information to the CERT/CC, we update this section and note the changes in our revision history. If a particular vendor is not listed below, we have not received their comments. Cyrusoft International, Inc. Mulberry does not use Internet Explorer to render HTML within Mulberry itself and is not vulnerable to these kinds of problems. Users can save HTML attachments to disk and then view those in browsers susceptible to this problem, but this requires the direct intervention of the user to explicitly save to disk - simply viewing HTML in Mulberry does not expose users to these kinds of problems. Our HTML rendering is a basic styled-text only renderer that does not execute any form of scripts. This is true on all the platforms we support: Win32, Mac OS (Classic & X), Solaris, linux. An official statement about this is available on our website at: http://www.cyrusoft.com/mulberry/htmlsecurity.html Lotus Development Corporation Notes does not use IE to render HTML-formatted mail messages. Microsoft Corporation Please see the advisory (MS01-020, "Incorrect MIME Header Can Cause IE to Execute E-mail Attachment") related to this issue at: http://www.microsoft.com/technet/security/bulletin/MS01-020.asp A patch is available for this issue at: http://www.microsoft.com/windows/ie/download/critical/Q290108/default.asp Netscape Communications Corporation Netscape is currently investigating the impact this vulnerability, if any, has on users of the Netscape browser. Opera Software Opera does not use Internet Explorer or any other external software to render HTML. QUALCOMM Incorporated It is unclear at this time what impact, if any, this vulnerability has on Eudora clients. Appendix B. - References 1. Havrilla, J., and Hernan, S., "CERT Vulnerability Note VU#980499: Certain MIME types can cause Internet Explorer to execute arbitrary code when rendering HTML", March 2001. https://www.kb.cert.org/vuls/id/980499 _________________________________________________________________ Microsoft has acknowledged Juan Carlos Cuartango for bringing this issue to their attention. This document was written by Jeffrey S. Havrilla and Shawn V. Hernan. If you have feedback, comments, or additional information about this issue, please send us email. ______________________________________________________________________ This document is available from: http://www.cert.org/advisories/CA-2001-06.html ______________________________________________________________________ CERT/CC Contact Information Email: cert@cert.org Phone: +1 412-268-7090 (24-hour hotline) Fax: +1 412-268-6989 Postal address: CERT Coordination Center Software Engineering Institute Carnegie Mellon University Pittsburgh PA 15213-3890 U.S.A. CERT personnel answer the hotline 08:00-20:00 EST(GMT-5) / EDT(GMT-4) Monday through Friday; they are on call for emergencies during other hours, on U.S. holidays, and on weekends. Using encryption We strongly urge you to encrypt sensitive information sent by email. Our public PGP key is available from http://www.cert.org/CERT_PGP.key If you prefer to use DES, please call the CERT hotline for more information. Getting security information CERT publications and other security information are available from our web site http://www.cert.org/ To subscribe to the CERT mailing list for advisories and bulletins, send email to majordomo@cert.org. Please include in the body of your message subscribe cert-advisory * "CERT" and "CERT Coordination Center" are registered in the U.S. Patent and Trademark Office. ______________________________________________________________________ NO WARRANTY Any material furnished by Carnegie Mellon University and the Software Engineering Institute is furnished on an "as is" basis. Carnegie Mellon University makes no warranties of any kind, either expressed or implied as to any matter including, but not limited to, warranty of fitness for a particular purpose or merchantability, exclusivity or results obtained from use of the material. Carnegie Mellon University does not make any warranty of any kind with respect to freedom from patent, trademark, or copyright infringement. _________________________________________________________________ Conditions for use, disclaimers, and sponsorship information Copyright 2001 Carnegie Mellon University. Revision History April 03, 2001: Initial release -----BEGIN PGP SIGNATURE----- Version: PGP for Personal Privacy 5.0 Charset: noconv iQCVAwUBOsoNNQYcfu8gsZJZAQFd3gQAkCKdIcdKJ/gaii0odrJdM/jlZUv7MYYf R8LUHkV1dUTxEI/SRrKtAoEsf/UVVgZI4PGBB/pyptkmSv2axMWf4AD1Ubful712 ojVaHG7hJuV5RNiw2yE/R4AoWZ5GbdaQByYWpCB+OfwNzsz/7MYibjI6xUtvqRvV JxYMB6q5TqM= =B0Bv -----END PGP SIGNATURE-----