-----BEGIN PGP SIGNED MESSAGE----- - ---------------------------------------------------------------------- Title: 13 December 2001 Cumulative Patch for IE Date: 13 December 2001 Software: Internet Explorer Impact: Run Code of an Attacker's Choice Max Risk: Critical Bulletin: MS01-058 Microsoft encourages customers to review the Security Bulletin at: http://www.microsoft.com/technet/security/bulletin/MS01-058.asp. - ---------------------------------------------------------------------- Issue: ====== This is a cumulative patch that, when installed, eliminates all previously discussed security vulnerabilities affecting IE 5.5 and IE 6. In addition, it eliminates three newly discovered vulnerabilities. - The first vulnerability involves a flaw in the handling of the Content-Disposition and Content-Type header fields in an HTML. stream. These fields, the hosting URL, and the hosted file data determine how a file is handled upon download in Internet Explorer. A security vulnerability exists because, if an attacker altered the HTML header information in a certain way, it could be possible to make IE believe that an executable file was actually a different type of file -- one that it is appropriate to simply open without asking the user for confirmation. This could enable the attacker to create a web page or HTML mail that, when opened, would automatically run an executable on the user's system. This vulnerability affects IE 6.0 only. It does not affect IE 5.5. - The second vulnerability is a newly discovered variant of the "Frame Domain Verification" vulnerability discussed in Microsoft Security Bulletin MS01-015. The vulnerability could enable a malicious web site operator to open two browser windows, one in the web site's domain and the other on the user's local file system, and to pass information from the latter to the former. This could enable the web site operator to read, but not change, any file on the user's local computer that could be opened in a browser window. This vulnerabilty affects both IE 5.5 and 6.0. - The third vulnerability involves a flaw related to the display of file names in the File Download dialogue box. When a file download is initiated, a dialogue provides the name of the file. However, in some cases, it would be possible for an attacker to misrepresent the name of the file in the dialogue. This could be invoked from a web page or in an HTML email in an attempt to fool users into accepting unsafe file types from a trusted source. This vulnerabilty affects both IE 5.5 and 6.0. Mitigating Factors: ==================== File Execution Vulnerability: - The vulnerability could not be exploited if File Downloads have been disabled in the Security Zone from which the file is being received. In most attempts to maliciously exploit this vulnerability the file would be received from the Internet or Intranet zone. Therefore, disabling File Downloads in these zones can protect customers. This is not the default setting for either of these zone, however. - This affects IE 6.0 only. Frame Domain Verification Variant: - The vulnerability could only be used to view files. It could not be used to create, delete, modify or execute them. - The vulnerability would only allow an attacker to read files that can be can be opened in a browser window, such as image files, HTML files and text files. Other file file types, such as binary files, executable files, Word documents, and so forth, could not be read. - The attacker would have to have knowledge of the exact file name and location in other to successfully read the file on the local system. File Name Spoofing Vulnerability: - The determination on choosing to accept a file download from an Internet site should always be based on the trustworthiness of the source and not on the file type. File downloads should never be accepted from an untrusted source, no matter how harmless the type may appear to be. Risk Rating: ============ - Internet systems: Critical - Intranet systems: Critical - Client systems: Critical Patch Availability: =================== - A patch is available to fix this vulnerability. Please read the Security Bulletin at http://www.microsoft.com/technet/security/bulletin/ms01-058.asp for information on obtaining this patch. Acknowledgment: =============== - Jouko Pynnonen of Oy Online Solutions Ltd (http://www.solutions.fi/index.cgi/?lang=eng) - --------------------------------------------------------------------- THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. 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This archive was generated by hypermail 2b30 : Mon Dec 17 2001 - 19:26:15 PST