Microsoft Security Bulletin MS05-038 - Critical

• In a Web-based attack scenario, an attacker would have to host a Web site that contains a Web page that is used to exploit this vulnerability. An attacker could also try to compromise a Web site and have it display malicious content. An attacker would have no way to force users to visit a Web site. Instead, an attacker would have to persuade them to visit the Web site, typically by getting them to click a link that takes them to the attacker's site or to a site that has been compromised by the attacker.
• An attacker who successfully exploited this vulnerability could gain the same user rights as the local user. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.
• By default, Internet Explorer on Windows Server 2003 runs in a restricted mode that is known as Enhanced Security Configuration. This mode mitigates this vulnerability where the e-mail vector is concerned although clicking on a link would still put users at risk. In Windows Server 2003, Microsoft Outlook Express uses plain text for reading and sending messages by default. When replying to an e-mail message that is sent in another format, the response is formatted in plain text. See the FAQ section of this vulnerability for more information about Internet Explorer Enhanced Security Configuration.

Microsoft has tested the following workarounds. While these workarounds will not correct the underlying vulnerability, they help block known attack vectors. When a workaround reduces functionality, it is identified in the following section.

• Read e-mail messages in plain text format if you are using Microsoft Outlook 2002 or a later version, or Outlook Express 6 SP1 or a later version, to help protect yourself from the HTML e-mail attack vector.

  Microsoft Outlook 2002 users who have applied Office XP Service Pack 1 or a later version and Microsoft Outlook Express 6 users who have applied Internet Explorer 6 Service Pack 1 or a later version can enable this setting and view e-mail messages that are not digitally signed or e-mail messages that are not encrypted in plain text only.

  Digitally signed e-mail messages or encrypted e-mail messages are not affected by the setting and may be read in their original formats. For more information about how to enable this setting in Outlook 2002, see Microsoft Knowledge Base Article 307594.

  For information about this setting in Outlook Express 6, see Microsoft Knowledge Base Article 291387.

  Impact of Workaround: E-mail messages that are viewed in plain text format will not contain pictures, specialized fonts, animations, or other rich content. Additionally:

  • The changes are applied to the preview pane and to open messages.
  • Pictures become attachments so that they are not lost.
  • Because the message is still in Rich Text or HTML format in the store, the object model (custom code solutions) may behave unexpectedly.

What is the scope of the vulnerability?
If a user is logged on with administrative user rights, an attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

What causes the vulnerability?
When Internet Explorer displays a specially formed JPEG image, it may corrupt system memory in such a way that an attacker could execute arbitrary code.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could take complete control of the affected system.

How could an attacker exploit the vulnerability?
An attacker could exploit this vulnerability by creating a malicious Web page or an HTML e-mail message and then persuading the user to visit the page or to view the HTML e-mail message. If the user visited the page or viewed the e-mail message, the attacker could access information from other Web sites, could access local files in predetermined locations on the system, or could cause malicious code to run in the security context of the locally logged on user. An attacker could also try to compromise a Web site and have it display malicious content.

What systems are primarily at risk from the vulnerability?
This vulnerability requires that a user is logged on and reading e-mail or visiting Web sites for any malicious action to occur. Therefore, any systems where e-mail is read or where Internet Explorer is used frequently, such as workstations or terminal servers, are at the most risk from this vulnerability. Systems that are not typically used to read e-mail or to visit Web sites, such as most server systems, are at a reduced risk.

I am running Internet Explorer on Windows Server 2003. Does this mitigate this vulnerability?
Yes. By default, Internet Explorer on Windows Server 2003 runs in a restricted mode that is known as Enhanced Security Configuration. This mode mitigates this vulnerability where the e-mail vector is concerned although clicking on a link would still put users at risk. In Windows Server 2003, Microsoft Outlook Express uses plain text for reading and sending messages by default. When replying to an e-mail message that is sent in another format, the response is formatted in plain text.

What is Internet Explorer Enhanced Security Configuration?
Internet Explorer Enhanced Security Configuration is a group of preconfigured Internet Explorer settings that reduce the likelihood of a user or of an administrator downloading and running malicious Web content on a server. Internet Explorer Enhanced Security Configuration reduces this risk by modifying many security-related settings. This includes the settings on the Security tab and the Advanced tab in the Internet Options dialog box. Some of the important modifications include the following:

• Security level for the Internet zone is set to High. This setting disables scripts, ActiveX controls, Microsoft Java Virtual Machine (MSJVM), HTML content, and file downloads.
• Automatic detection of intranet sites is disabled. This setting assigns all intranet Web sites and all Universal Naming Convention (UNC) paths that are not explicitly listed in the Local intranet zone to the Internet zone.
• Install On Demand and non-Microsoft browser extensions are disabled. This setting prevents Web pages from automatically installing components and prevents non-Microsoft extensions from running.
• Multimedia content is disabled. This setting prevents music, animations, and video clips from running.

What does the update do?
The update removes the vulnerability by modifying the way that Internet Explorer validates the length of a message before it passes the message to the allocated buffer.

When this security bulletin was issued, had this vulnerability been publicly disclosed?
Yes. This vulnerability has been publicly disclosed. It has been assigned Common Vulnerability and Exposure number CAN-2005-1988.

When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited?
No. Microsoft had not received any information to indicate that this vulnerability had been publicly used to attack customers and had not seen any examples of proof of concept code published when this security bulletin was originally issued.

• In a Web-based attack scenario, an attacker would have to host a Web site that contains a Web page that is used to exploit this vulnerability. An attacker could also attempt to compromise a Web site to have it display a Web page that contains malicious content. An attacker would have no way to force users to visit a Web site. Instead, an attacker would have to persuade them to visit the Web site, typically by getting them to click a link that takes them to the attacker's site or to a site that has been compromised by the attacker.
• An attacker who successfully exploited this vulnerability could gain the same user rights as the local user. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.
• The Restricted sites zone helps reduce attacks that could try to exploit this vulnerability by preventing Active Scripting and ActiveX controls from being used when reading HTML e-mail messages. However, if a user clicks a link in an e-mail message, they could still be vulnerable to this issue through the Web-based attack scenario
  
  By default, Outlook Express 6, Outlook 2002, and Outlook 2003 open HTML e-mail messages in the Restricted sites zone. Additionally, Outlook 98 and Outlook 2000 open HTML e-mail messages in the Restricted sites zone if the Outlook E-mail Security Update has been installed. Outlook Express 5.5 Service Pack 2 opens HTML e-mail messages in the Restricted sites zone if Microsoft Security Bulletin MS04-018 has been installed.
• By default, Internet Explorer on Windows Server 2003 runs in a restricted mode that is known as Enhanced Security Configuration. This mode mitigates this vulnerability. See the FAQ section of this security update for more information about Internet Explorer Enhanced Security Configuration.
• Windows XP Service Pack 2 introduced a security enhancement known as the Local Machine zone lockdown. This security enhancement mitigates this vulnerability when the Local Machine Zone is the target of an attack. See the FAQ section of this security update for more information about the Local Machine zone lockdown.

Microsoft has tested the following workarounds. While these workarounds will not correct the underlying vulnerability, they help block known attack vectors. When a workaround reduces functionality, it is identified in the following section.

• Set Internet and Local intranet security zone settings to “High” to prompt before running ActiveX controls and Active Scripting in these zones.

  You can help protect against this vulnerability by changing your settings for the Internet security zone to prompt before running ActiveX controls and Active Scripting. You can do this by setting your browser security to High.

  To raise the browsing security level in Microsoft 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 high security setting.

  Impact of Workaround: There are side effects to prompting before running ActiveX controls. Many Web sites that are on the Internet or on an intranet use ActiveX 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. Prompting before running ActiveX controls 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 ActiveX controls. If you do not want to be prompted for all these sites, use the "Restrict Web sites to only your trusted Web sites" workaround.

• Configure Internet Explorer to prompt before running ActiveX controls or disable ActiveX controls in the Internet and Local intranet security zone

  You can help protect against this vulnerability by changing your settings to prompt before running ActiveX controls only. 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 ActiveX controls and plug-ins section, under Run ActiveX controls and plug-ins, click Prompt.
  5. In the Scripting section, under Active Scripting, click Prompt, and then click OK.
  6. Click Local intranet, and then click Custom Level.
  7. Under Settings, in the ActiveX controls and plug-ins section, under Run ActiveX controls and plug-ins, click Prompt.
  8. In the Scripting section, under Active Scripting, click Prompt.
  9. Click OK two times to return to Internet Explorer.

  Impact of Workaround: There are side effects to prompting before running ActiveX controls. Many Web sites that are on the Internet or on an intranet use ActiveX 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. Prompting before running ActiveX controls 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 ActiveX controls. If you do not want to be prompted for all these sites, use the "Restrict Web sites to only your trusted Web sites" workaround.

• Restrict Web sites to only your trusted Web sites.

  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 Internet Explorer's 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.

  Add any sites that you trust not to take malicious action on your computer. One in particular that you may want to add is "*.windowsupdate.microsoft.com" (without the quotation marks). This is the site that will host the update, and it requires an ActiveX control to install the update.

What is the scope of the vulnerability?
This is a cross-domain vulnerability that could allow information disclosure or remote code execution. If a user is logged on with administrative privileges, an attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full privileges. Users whose accounts are configured to have fewer privileges on the system could be less impacted than users who operate with administrative privileges.

What causes the vulnerability?
The process by which certain URLs are interpreted when browsing from a Web page to a Web folder view using WebDAV. This process is handled by the Web Folder Behaviors in Internet Explorer. URLs are not properly validated by the Internet Explorer cross-domain security model.

What are Web Folder Behaviors?
Web Folder Behaviors are available in Microsoft Internet Explorer 5 and later versions. Web Folder Behaviors allow users to browse to a folder view, and include support for Distributed Authoring and Versioning (DAV) and Web Extender Client (WEC) protocols. For more information about Web Folder Behaviors, see the product documentation.

What are Internet Explorer security zones?
Internet Explorer security zones are part of a system that divides online content into categories or zones, based on the trustworthiness of the content. Specific Web domains can be assigned to a zone, depending on how much trust is put in the content of each domain. The zone then restricts the capabilities of the Web content, based on the zone's policy. By default, most Internet domains are treated as part of the Internet zone. By default, the policy of the Internet zone prevents scripts and other active code from accessing resources on the local system.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could run malicious script code in the Local Machine security zone or another security zone or domain in Internet Explorer. This could allow an attacker to take complete control of the affected system.

How could an attacker exploit the vulnerability?
An attacker could exploit this vulnerability by creating a malicious Web page and then persuading the user to visit this page When the user visited the page and interacted with the Web page, the attacker could access information from other Web sites, could access local files on the system, or could cause script to run in the security context of the Local Machine zone or another security zone or domain.

What systems are primarily at risk from the vulnerability?
This vulnerability requires that a user view a Web site for malicious action to occur and accept a prompt for adding an Internet Explorer favorite to their system. Therefore, any systems where Internet Explorer is used frequently, such as workstations or terminal servers, are at the most risk from this vulnerability. Systems that are not typically used to visit Web sites, such as most server systems, are at a reduced risk.

I am running Internet Explorer on Windows Server 2003. Does this mitigate this vulnerability?
Yes. By default, Internet Explorer on Windows Server 2003 runs in a restricted mode that is known as Enhanced Security Configuration. This mode mitigates this vulnerability.

What is Internet Explorer Enhanced Security Configuration?
Internet Explorer Enhanced Security Configuration is a group of preconfigured Internet Explorer settings that reduce the likelihood of a user or of an administrator downloading and running malicious Web content on a server. Internet Explorer Enhanced Security Configuration reduces this risk by modifying many security-related settings. This includes the settings on the Security tab and the Advanced tab in the Internet Options dialog box. Some of the important modifications include the following:

• Security level for the Internet zone is set to High. This setting disables scripts, ActiveX controls, Microsoft Java Virtual Machine (MSJVM), HTML content, and file downloads.
• Automatic detection of intranet sites is disabled. This setting assigns all intranet Web sites and all Universal Naming Convention (UNC) paths that are not explicitly listed in the Local intranet zone to the Internet zone.
• Install On Demand and non-Microsoft browser extensions are disabled. This setting prevents Web pages from automatically installing components and prevents non-Microsoft extensions from running.
• Multimedia content is disabled. This setting prevents music, animations, and video clips from running.

I am running Internet Explorer on Windows XP Service Pack 2. Does this mitigate this vulnerability?
Yes. Windows XP Service Pack 2 introduced a security enhancement known as the Local Machine zone lockdown that mitigates this vulnerability when the Local Machine Zone is the target of an attack.

What is the Local Machine zone lockdown?
In Windows XP Service Pack 2, all local files and content that are processed by Internet Explorer have additional security restrictions applied to them in the Local Machine zone. This feature restricts HTML in the Local Machine zone. This feature also restricts HTML that is hosted in Internet Explorer. These restrictions help mitigate attacks where the Local Machine zone is used as an attack vector to load malicious HTML code.

Because of this change, ActiveX script in local HTML pages that is viewed inside Internet Explorer will not run. Also, script in local HTML pages that is viewed inside Internet Explorer prompts the user for permission to run.

Are Windows 98, Windows 98 Second Edition or Windows Millennium Edition critically affected by this vulnerability?
No. Although Windows 98, Windows 98 Second Edition, and Windows Millennium Edition do contain the affected component, the vulnerability is not critical. For more information about severity ratings, visit the following Web site.

What does the update do?
The update removes the vulnerability by making sure that the Internet Explorer cross-domain security model is enforced when navigating from a Web page to a Web folder view in Internet Explorer.

When this security bulletin was issued, had this vulnerability been publicly disclosed?
No. Microsoft received information about this vulnerability through responsible disclosure.

• In a Web-based attack scenario, an attacker would have to host a Web site that contains a Web page that is used to exploit this vulnerability. An attacker would have no way to force users to visit a malicious Web site. Instead, an attacker would have to persuade them to visit the Web site, typically by getting them to click a link that takes them to the attacker's Web site.
• An attacker who successfully exploited this vulnerability could gain the same user rights as the local user. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.
• The Restricted sites zone helps reduce attacks that could try to exploit this vulnerability by preventing ActiveX controls from being used when reading HTML e-mail messages. However, if a user clicks a link in an e-mail message, they could still be vulnerable to this issue through the Web-based attack scenario.
  
  By default, Outlook Express 6, Outlook 2002, and Outlook 2003 open HTML e-mail messages in the Restricted sites zone. Additionally, Outlook 98 and Outlook 2000 open HTML e-mail messages in the Restricted sites zone if the Outlook E-mail Security Update has been installed. Outlook Express 5.5 Service Pack 2 opens HTML e-mail messages in the Restricted sites zone if Microsoft Security Bulletin MS04-018 has been installed.
• By default, Internet Explorer on Windows Server 2003 runs in a restricted mode that is known as Enhanced Security Configuration. This mode mitigates this vulnerability. See the FAQ section of this security update for more information about Internet Explorer Enhanced Security Configuration.

Microsoft has tested the following workarounds. While these workarounds will not correct the underlying vulnerability, they help block known attack vectors. The workarounds are mutually exclusive. Users need only apply one workaround. When a workaround reduces functionality, it is identified in the following section.

• Set Internet and Local intranet security zone settings to “High” to prompt before running ActiveX controls in these zones

  You can help protect against this vulnerability by changing your settings for the Internet security zone to prompt before running ActiveX controls. You can do this by setting your browser security to High.

  To raise the browsing security level in Microsoft 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.

  Repeat steps 1 through 3 for the Local intranet security zone by clicking the Local intranet icon.

  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: User will be prompted prior to running ActiveX controls unless the Web site is in the user’s list of trusted sites.

• Configure Internet Explorer to prompt before running ActiveX controls or disable ActiveX controls in the Internet and Local intranet security zone

  You can help protect against this vulnerability by changing your settings to prompt before running ActiveX controls or disable ActiveX controls in the Internet and Local intranet security zone. To do this, 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. Click Custom Level.
  4. Under Settings, in the ActiveX controls and plug-ins section, under Run ActiveX controls and plug-ins, click Prompt or Disable, and then click OK.
  5. Click Local intranet, and then click Custom Level.
  6. Under Settings, in the ActiveX controls and plug-ins section, under Run ActiveX controls and plug-ins, click Prompt or Disable, and then click OK.
  7. Click OK two times to return to Internet Explorer.

  Impact of Workaround: There are side effects to prompting before running ActiveX controls. Many Web sites that are on the Internet or on an intranet use ActiveX 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. Prompting before running ActiveX controls 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 ActiveX controls.

What is the scope of the vulnerability?
This is a remote code execution vulnerability. An attacker who successfully exploited this vulnerability could remotely take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.

What causes the vulnerability?
When Internet Explorer tries to instantiate certain COM objects as ActiveX controls, the COM Objects may corrupt system memory in such a way that an attacker could execute arbitrary code.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could take complete control of the affected system. In a Web-based attack scenario, an attacker would host a Web site that exploits this vulnerability. An attacker would have no way to force users to visit a malicious Web site. Instead, an attacker would have to persuade them to visit the Web site, typically by getting them to click a link that takes them to the attacker's site. It could also be possible to display malicious Web content by using banner advertisements or by using other methods to deliver Web content to affected systems.

How could an attacker exploit the vulnerability?
An attacker could host a malicious Web site that is designed to exploit this vulnerability through Internet Explorer and then persuade a user to view the Web site.

What systems are primarily at risk from the vulnerability?
This vulnerability requires that a user is logged on and reading e-mail messages or by visiting Web sites for any malicious action to occur. Therefore, any systems where e-mail messages are read or where Internet Explorer is used frequently, such as workstations or terminal servers, are at the most risk from this vulnerability.

Are Windows 98, Windows 98 Second Edition or Windows Millennium Edition critically affected by this vulnerability?
Yes. Windows 98, Windows 98 Second Edition, and Windows Millennium Edition are critically affected by this vulnerability. The security updates are available from the Windows Update Web site. For more information about severity ratings, visit the following Web site.

What does the update do?
Because not all COM objects are designed to be accessed through Internet Explorer, this update sets the kill bit for a list of Class identifiers (CLSIDs) in COM objects that have been found to exhibit similar behavior to the JVIEW Profiler vulnerability that is addressed in Microsoft Security Bulletin MS05-037. To help protect customers, this update prevents these CLSIDs from being instantiated in Internet Explorer. For more information about kill bits, see Microsoft Knowledge Base Article 240797.

The Class Identifiers and corresponding COM Objects are:

When this security bulletin was issued, had this vulnerability been publicly disclosed?
The vulnerability addressed in Microsoft Security Bulletin MS05-037 had been publicly disclosed. However, none of the CLSIDs that are addressed in this bulletin had been publicly disclosed.

When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited?
When the security bulletin was released, Microsoft had received information that the vulnerability that is addressed in Microsoft Security Bulletin MS05-037 had been exploited. Microsoft had not received information that any of the CLSIDs that are addressed in this bulletin had been exploited.

Does applying this security update help protect customers from the code that has been published publicly that attempts to exploit this vulnerability?
This security update addresses the vulnerability that is currently being exploited and that was addressed in Microsoft Security Bulletin MS05-037.