===================================================================== CERT-Renater Note d'Information No. 2011/VULN073 _____________________________________________________________________ DATE : 31/01/2011 HARDWARE PLATFORM(S) : / OPERATING SYSTEM(S) : Windows XP, Windows Server 2003, Windows Vista, Windows Server 2008, Windows 7. ====================================================================== http://www.microsoft.com/technet/security/advisory/2501696.mspx ______________________________________________________________________ Microsoft Security Advisory (2501696) Vulnerability in MHTML Could Allow Information Disclosure Published: January 28, 2011 Version: 1.0 General Information Executive Summary Microsoft is investigating new public reports of a vulnerability in all supported editions of Microsoft Windows. The vulnerability could allow an attacker to cause a victim to run malicious scripts when visiting various Web sites, resulting in information disclosure. This impact is similar to server- side cross-site scripting (XSS) vulnerabilities. Microsoft is aware of published information and proof-of-concept code that attempts to exploit this vulnerability. At this time, Microsoft has not seen any indications of active exploitation of the vulnerability. The vulnerability exists due to the way MHTML interprets MIME-formatted requests for content blocks within a document. It is possible under certain conditions for this vulnerability to allow an attacker to inject a client- side script in the response of a Web request run in the context of the victim's Internet Explorer. The script could spoof content, disclose information, or take any action that the user could take on the affected Web site on behalf of the targeted user. We are actively working with partners in our Microsoft Active Protections Program (MAPP) to provide information that they can use to provide broader protections to customers. We are collaborating with Service Providers to investigate server-side workarounds, but we recommend that customers apply one or more of the client- side workarounds provided in the Suggested Actions section of this advisory to help block potential attack vectors regardless of the service. Upon completion of this investigation, Microsoft will take the appropriate action to help protect our customers. This may include providing a security update through our monthly release process or providing an out-of-cycle security update, depending on customer needs. Advisory Details Issue References For more information about this issue, see the following references: References Identification CVE Reference CVE-2011-0096 Microsoft Knowledge Base Article 2501696 Affected Software Windows XP Service Pack 3 Windows XP Professional x64 Edition Service Pack 2 Windows Server 2003 Service Pack 2 Windows Server 2003 x64 Edition Service Pack 2 Windows Server 2003 with SP2 for Itanium-based Systems Windows Vista Service Pack 1 and Windows Vista Service Pack 2 Windows Vista x64 Edition Service Pack 1 and Windows Vista x64 Edition Service Pack 2 Windows Server 2008 for 32-bit Systems and Windows Server 2008 for 32-bit Systems Service Pack 2** Windows Server 2008 for x64-based Systems and Windows Server 2008 for x64-based Systems Service Pack 2** Windows Server 2008 for Itanium-based Systems and Windows Server 2008 for Itanium-based Systems Service Pack 2 Windows 7 for 32-bit Systems Windows 7 for x64-based Systems Windows Server 2008 R2 for x64-based Systems** Windows Server 2008 R2 for Itanium-based Systems **Server Core installation not affected. The vulnerability described in this advisory does not affect supported editions of Windows Server 2008 or Windows Server 2008 R2 as indicated, when installed using the Server Core installation option. For more information on this installation option, see the TechNet articles, Managing a Server Core Installation and Servicing a Server Core Installation. Note that the Server Core installation option does not apply to certain editions of Windows Server 2008 and Windows Server 2008 R2; see Compare Server Core Installation Options. Mitigating Factors and Suggested Actions Mitigating Factors Mitigation refers to a setting, common configuration, or general best-practice, existing in a default state, that could reduce the severity of exploitation of a vulnerability. The following mitigating factors may be helpful in your situation: By default, Internet Explorer on Windows Server 2003, Windows Server 2008, and Windows Server 2008 R2 runs in a restricted mode that is known as Enhanced Security Configuration. This mode mitigates this vulnerability. By default, all supported versions of Microsoft Outlook, Microsoft Outlook Express, and Windows Mail open HTML e-mail messages in the Restricted sites zone, which disables script and ActiveX controls, removing the risk of an attacker being able to use this vulnerability to execute malicious code. If a user clicks a link in an e-mail message, the user could still be vulnerable to exploitation of this vulnerability through the Web-based attack scenario. In a Web-based attack scenario, a Web site could contain a specially crafted link (MHTML:) that is used to exploit this vulnerability. An attacker would have to convince users to visit the Web site and open a specially crafted URL, typically by getting them to click a link in an e-mail message or Instant Messenger message that takes users to the attacker's Web site, and then convincing them to click the specially crafted link. Suggested Actions * Enable the MHTML protocol lockdown Note Workarounds refer to a setting or configuration change that does not correct the underlying issue but would help block known attack vectors before a security update is available. Microsoft has tested the following workaround and states in the discussion whether the workaround reduces functionality. Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk. Note See Microsoft Knowledge Base Article 2501696 to use the automated Microsoft Fix it solution to enable and disable this workaround. To lockdown the MHTML protocol, paste the following text in a text editor such as Notepad. Then, save the file by using the .reg file name extension. For 32-bit editions of Microsoft Windows: Windows Registry Editor Version 5.00 [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_PROTOCOL_LOCKDOWN] "explorer.exe"=dword:00000001 "iexplore.exe"=dword:00000001 "*"=dword:00000001 [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\RestrictedProtocols] [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\RestrictedProtocols\1] "mhtml"="mhtml" [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\RestrictedProtocols\2] "mhtml"="mhtml" [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\RestrictedProtocols\3] "mhtml"="mhtml" [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\RestrictedProtocols\4] "mhtml"="mhtml" For 64-bit editions of Microsoft Windows: Windows Registry Editor Version 5.00 [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_PROTOCOL_LOCKDOWN] "explorer.exe"=dword:00000001 "iexplore.exe"=dword:00000001 "*"=dword:00000001 [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\RestrictedProtocols] [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\RestrictedProtocols\1] "mhtml"="mhtml" [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\RestrictedProtocols\2] "mhtml"="mhtml" [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\RestrictedProtocols\3] "mhtml"="mhtml" [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\RestrictedProtocols\4] "mhtml"="mhtml" [HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_PROTOCOL_LOCKDOWN] "explorer.exe"=dword:00000001 "iexplore.exe"=dword:00000001 "*"=dword:00000001 [HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Internet Settings\RestrictedProtocols] [HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Internet Settings\RestrictedProtocols\1] "mhtml"="mhtml" [HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Internet Settings\RestrictedProtocols\2] "mhtml"="mhtml" [HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Internet Settings\RestrictedProtocols\3] "mhtml"="mhtml" [HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Internet Settings\RestrictedProtocols\4] "mhtml"="mhtml" You can apply this .reg file to individual systems by double-clicking it. You can also apply it across domains by using Group Policy. For more information about Group Policy, visit the following Microsoft Web sites: * Group Policy collection * What is Group Policy Object Editor * Core Group Policy tools and settings Impact of workaround. The MHTML protocol will be restricted to prevent the launch of script in all zones within an MHTML document. Any application that uses MHTML will be affected by this workaround. Script in standard HTML files is not affected by this workaround. How to undo the workaround. To reverse this workaround, paste the following text in a text editor such as Notepad. Then, save the file by using the .reg file name extension. * Set Internet and Local intranet security zone settings to "High" to block ActiveX Controls and Active Scripting in these zones Note Workarounds refer to a setting or configuration change that does not correct the underlying issue but would help block known attack vectors before a security update is available. Microsoft has tested the following workaround and states in the discussion whether the workaround reduces functionality. You can help protect against exploitation of this vulnerability by changing your settings for the Internet security zone to block ActiveX controls and Active Scripting. You can do this by setting your browser security to High. To raise the browsing security level in Internet Explorer, follow these steps: 1. On the Internet Explorer Tools menu, click Internet Options. 2. In the Internet Options dialog box, click the Security tab, and then click the Internet icon. 3. Under Security level for this zone, move the slider to High. This sets the security level for all Web sites you visit to High. Note If no slider is visible, click Default Level, and then move the slider to High. Note Setting the level to High may cause some Web sites to work incorrectly. If you have difficulty using a Web site after you change this setting, and you are sure the site is safe to use, you can add that site to your list of trusted sites. This will allow the site to work correctly even with the security setting set to High. Impact of workaround. There are side effects to blocking ActiveX Controls and Active Scripting. Many Web sites that are on the Internet or on an intranet use ActiveX or Active Scripting to provide additional functionality. For example, an online e-commerce site or banking site may use ActiveX Controls to provide menus, ordering forms, or even account statements. Blocking ActiveX Controls or Active Scripting is a global setting that affects all Internet and intranet sites. If you do not want to block ActiveX Controls or Active Scripting for such sites, use the steps outlined in "Add sites that you trust to the Internet Explorer Trusted sites zone". Add sites that you trust to the Internet Explorer Trusted sites zone After you set Internet Explorer to block ActiveX controls and Active Scripting in the Internet zone and in the Local intranet zone, you can add sites that you trust to the Internet Explorer Trusted sites zone. This will allow you to continue to use trusted Web sites exactly as you do today, while helping to protect yourself from this attack on untrusted sites. We recommend that you add only sites that you trust to the Trusted sites zone. To do this, follow these steps: 1. In Internet Explorer, click Tools, click Internet Options, and then click the Security tab. 2. In the Select a Web content zone to specify its current security settings box, click Trusted Sites, and then click Sites. 3. If you want to add sites that do not require an encrypted channel, click to clear the Require server verification (https:) for all sites in this zone check box. 4. In the Add this Web site to the zone box, type the URL of a site that you trust, and then click Add. 5. Repeat these steps for each site that you want to add to the zone. 6. Click OK two times to accept the changes and return to Internet Explorer. Note Add any sites that you trust not to take malicious action on your system. Two in particular that you may want to add are *.windowsupdate.microsoft.com and *.update.microsoft.com. These are the sites that will host the update, and it requires an ActiveX Control to install the update. * Configure Internet Explorer to prompt before running Active Scripting or to disable Active Scripting in the Internet and Local intranet security zone Note Workarounds refer to a setting or configuration change that does not correct the underlying issue but would help block known attack vectors before a security update is available. Microsoft has tested the following workaround and states in the discussion whether the workaround reduces functionality. You can help protect against exploitation of this vulnerability by changing your settings to prompt before running Active Scripting or to disable Active Scripting in the Internet and Local intranet security zone. To do this, follow these steps: 1. In Internet Explorer, click Internet Options on the Tools menu. 2. Click the Security tab. 3. Click Internet, and then click Custom Level. 4. Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK. 5. Click Local intranet, and then click Custom Level. 6. Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK. 7. Click OK two times to return to Internet Explorer. Note Disabling Active Scripting in the Internet and Local intranet security zones may cause some Web sites to work incorrectly. If you have difficulty using a Web site after you change this setting, and you are sure the site is safe to use, you can add that site to your list of trusted sites. This will allow the site to work correctly. Impact of workaround. There are side effects to prompting before running Active Scripting. Many Web sites that are on the Internet or on an intranet use Active Scripting to provide additional functionality. For example, an online e-commerce site or banking site may use Active Scripting to provide menus, ordering forms, or even account statements. Prompting before running Active Scripting is a global setting that affects all Internet and intranet sites. You will be prompted frequently when you enable this workaround. For each prompt, if you feel you trust the site that you are visiting, click Yes to run Active Scripting. If you do not want to be prompted for all these sites, use the steps outlined in "Add sites that you trust to the Internet Explorer Trusted sites zone". Add sites that you trust to the Internet Explorer Trusted sites zone After you set Internet Explorer to require a prompt before it runs ActiveX controls and Active Scripting in the Internet zone and in the Local intranet zone, you can add sites that you trust to the Internet Explorer Trusted sites zone. This will allow you to continue to use trusted Web sites exactly as you do today, while helping to protect you from this attack on untrusted sites. We recommend that you add only sites that you trust to the Trusted sites zone. To do this, follow these steps: 1. In Internet Explorer, click Tools, click Internet Options, and then click the Security tab. 2. In the Select a Web content zone to specify its current security settings box, click Trusted Sites, and then click Sites. 3. If you want to add sites that do not require an encrypted channel, click to clear the Require server verification (https:) for all sites in this zone check box. 4. In the Add this Web site to the zone box, type the URL of a site that you trust, and then click Add. 5. Repeat these steps for each site that you want to add to the zone. 6. Click OK two times to accept the changes and return to Internet Explorer. Note Add any sites that you trust not to take malicious action on your system. Two in particular that you may want to add are *.windowsupdate.microsoft.com and *.update.microsoft.com. These are the sites that will host the update, and it requires an ActiveX Control to install the update. ====================================================================== ========================================================= Les serveurs de référence du CERT-Renater http://www.urec.fr/securite http://www.cru.fr/securite http://www.renater.fr ========================================================= + CERT-RENATER | tel : 01-53-94-20-44 + + 23 - 25 Rue Daviel | fax : 01-53-94-20-41 + + 75013 Paris | email: certsvp@renater.fr + =========================================================