[ SOURCE: http://www.secureroot.com/security/advisories/9641794915.html ] Microsoft Security Bulletin (MS98-015) - ------------------------------------------------------------ Update available for "Untrusted Scripted Paste" Issue in Microsoft Internet Explorer 4.01 Originally Posted: October 16, 1998 Last Revised: October 16, 1998 Summary ======= Microsoft has released a patch that fixes a vulnerability involving scripted pastes that has been discovered with Internet Explorer 4.01 on Win32 and Win16 platforms. The vulnerability could make it possible for a malicious hacker to create a web site that, when visited, is able to use script to read a file on the user's system. The file must be in a location known to the malicious hacker. This has also been referred to as the "Cuartango" vulnerability. Microsoft highly recommends that users that have affected software installed on their systems should download and install the available patch as soon as possible. Issue ===== The "Untrusted Scripted Paste" issue involves a vulnerability in Internet Explorer that could allow a malicious hacker to circumvent certain Internet Explorer security safeguards. This vulnerability makes it possible for a malicious Web site operator to read the contents of a file on the user's computer if the hacker knows the exact name and path of the targeted file. This could also be used to view the contents of a file on the user's network to which the user has access, and whose direct path name is known by the attacker. The nature of this problem is that a script is able to use the Document.ExecCommand function to paste a filename into the file upload intrinsic control, which should only be possible by explicit user action. As a result, a subsequent form submission could send the file to a remote web site unbeknownst to the user if the user has disabled the default warning that is displayed when submitting unencrypted forms (see "Administrative Workaround" below for information on re-enabling this functionality). While there have not been any reports of customers being adversely affected by these problems, Microsoft is releasing a patch to address any risks posed by this issue. Affected Software Versions ========================== - Microsoft Internet Explorer 4.01 and 4.01 SP1 on Windows NT 4.0, Windows 95 - Microsoft Windows 98, with integrated Internet Explorer - Microsoft Internet Explorer 4.01 for Windows 3.1 and Windows NT 3.51 This vulnerability could also affect software that uses HTML functionality provided by Internet Explorer, even if Internet Explorer is not used as your default browser. All customers that have affected versions of Internet Explorer on their systems should install this patch, whether or not they use Internet Explorer for web browsing. This vulnerability does not affect Internet Explorer 3.x or 4.0 on any platform. This does not affect any Macintosh or UNIX versions of Internet Explorer. What Microsoft is Doing ======================= On October 16th Microsoft released a patch that fixes the problem identified. This patch is available for download from the sites listed below. Microsoft has sent this security bulletin to customers subscribing to the Microsoft Product Security Notification Service (see http://www.microsoft.com/security/bulletin.htm for more information about this free customer service). Microsoft has published the following Knowledge Base (KB) articles on this issue: - Microsoft Knowledge Base (KB) article Q169245, Update available for "Untrusted Scripted Paste" Issue http://support.microsoft.com/support/kb/articles/q169/2/45.asp What customers should do ======================== Microsoft highly recommends that users that have affected software installed on their systems should download and install the available patch as soon as possible. Complete URLs for each affected software version is given below. Windows 98 - ---------- Windows 98 customers can obtain the patch using Windows Update. To obtain this patch using Windows Update, launch Windows Update from the Windows Start Menu and click "Product Updates." When prompted, select 'Yes' to allow Windows Update to determine whether this patch and other updates are needed by your computer. If your computer does need this patch, you will find it listed under the "Critical Updates" section of the page. Internet Explorer 4.01 - ---------------------- Customers using Internet Explorer 4.01 can obtain the patch from the Internet Explorer Security web site, http://www.microsoft.com/ie/security/paste.htm Administrative workaround ========================= Microsoft strongly encourages customers to apply the patch. However, there are additional actions that can be taken to ensure safe computing: If the user has disabled the default warning that is displayed when submitting unencrypted forms, re-enabling this feature can provide additional protection. This warning prompt makes sure users are aware if a script attempts to submit data using forms. Users should be cautious if they see this warning when browsing and have not actually chosen to submit any data. To turn on this prompt: 1. From Internet Explorer, choose "Internet Options" form the "View" menu. 2. Click on the tab labeled "Security". 3. Click on "Internet Zone", then click "Customize Settings". 4. Scroll to "Submit non-encrypted form data" and click on "Prompt" (or "Disable" if you prefer). These same procedures should be followed for the "Restricted Sites" Zone. Additionally, users who cannot apply the patch immediately can disable Active Scripting technologies in Internet Explorer to protect themselves from this issue. Customers can use the Zones security feature in Internet Explorer 4 to disable Active Scripting (VBScript and JScript) in untrusted or unknown Internet sites, while still permitting known and trusted sites that use JScript and VBScript to work properly. To turn off Active Scripting for the "Internet" Zone: 1. From Internet Explorer, choose "Internet Options" from the "View" menu. 2. Click on the tab labeled "Security". 3. Click on "Internet Zone", then click "Customize Settings". 4. Scroll to the bottom of the list and click on "Disable" under the "Active Scripting" setting. 5. These same procedures should be followed for the "Restricted Sites" Zone. Sites that are trusted to use JScript and VBScript can be added to the Trusted Zones list. For more information on using Zones, please see the Online Help included with Internet Explorer. More Information ================ Please see the following references for more information related to this issue. - Microsoft Security Bulletin MS98-015, Update available for "Untrusted Scripted Paste" Issue in Microsoft Internet Explorer 4.01, (the Web posted version of this bulletin), http://www.microsoft.com/security/bulletins/ms98-015.htm - Microsoft Knowledge Base (KB) article Q169245, Update available for "Untrusted Scripted Paste" Issue http://support.microsoft.com/support/kb/articles/q169/2/45.asp Obtaining Support on this Issue =============================== This is a supported patch for Internet Explorer. If you have problems installing this patch or require technical assistance with this patch, please contact Microsoft Technical Support. For information on contacting Microsoft Technical Support, please see http://support.microsoft.com/support/contact/default.asp Acknowledgements ================ This bug was first reported by Juan Carlos Garcia Cuartango from Spain. Revisions ========= - October 16, 1998: Bulletin Created For additional security-related information about Microsoft products, please visit http://www.microsoft.com/security - ------------------------------------------------------------ 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. 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