Microsoft Security Bulletin MS05-020

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, Outlook Express 6, Outlook 2002, and Outlook 2003 open HTML e-mail messages in the Restricted sites zone. Additionally, Outlook 2000 opens 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. The Restricted sites zone helps reduce attacks that could try to exploit this vulnerability.

The risk of attack from the HTML e-mail vector can be significantly reduced if you meet all the following conditions:

The vulnerability could not be exploited automatically through e-mail. For an attack to be successful, a user must open an attachment that is sent in an e-mail message or click a link in an e-mail message.

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 vulnerability for more information about Internet Explorer Enhanced Security Configuration.

Set Internet and Local intranet security zone settings to “High” to prompt before running 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 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:

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. See the “Restrict Web sites to only your trusted Web sites” workaround for information about how you can add sites to the Trusted sites zone.

Alternatively, you can change your settings to prompt before running Active Scripting only. To do this, follow these steps:

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. Prompting before running Active Scripting 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 Active Scripting. 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 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:

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.

Install the update that is described in Microsoft Security Bulletin MS04-018 if you are using Outlook Express 5.5 SP2.

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.

Customers who use one or more of these products could be at a reduced risk from an e-mail-borne attack that tries to exploit this vulnerability unless the user clicks a malicious link in the e-mail message.

Read e-mail messages in plain text format if you are using 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 security level for the Internet zone is set to High. This setting disables scripts, ActiveX controls, Microsoft Java Virtual Machine (MSJVM), 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.

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, Outlook Express 6, Outlook 2002, and Outlook 2003 open HTML e-mail messages in the Restricted sites zone. Additionally, Outlook 2000 opens 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. The Restricted sites zone helps reduce attacks that could try to exploit this vulnerability.

The risk of attack from the HTML e-mail vector can be significantly reduced if you meet all the following conditions:

The vulnerability could not be exploited automatically through e-mail. For an attack to be successful, a user must click a malicious link that is sent in an e-mail message.

Set Internet and Local intranet security zone settings to “High” to prompt before running 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 Active Scripting. You can do this by setting your browser security to High.

Note This workaround provides limited protection and there are known attack vectors that do not rely on Active Scripting.

To raise the browsing security level in Microsoft Internet Explorer, follow these steps:

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.

Alternatively, you can change your settings to prompt before running Active Scripting only. To do this, follow these steps:

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. Prompting before running Active Scripting 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 Active Scripting. 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 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:

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.

Install the update that is described in Microsoft Security Bulletin MS04-018 if you are using Outlook Express 5.5 SP2.

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.

Customers who use one or more of these products could be at a reduced risk from an e-mail-borne attack that tries to exploit this vulnerability unless the user clicks a malicious link in the e-mail message.

Read e-mail messages in plain text format if you are using 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:

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. A user would then have to click through a series of Content Advisor setup windows for an attack to be successful.

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, Outlook Express 6, Outlook 2002, and Outlook 2003 open HTML e-mail messages in the Restricted sites zone. Additionally, Outlook 2000 opens 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. The Restricted sites zone helps reduce attacks that could try to exploit this vulnerability.

The risk of attack from the HTML e-mail vector can be significantly reduced if you meet all the following conditions:

The vulnerability could not be exploited automatically through e-mail. For an attack to be successful, a user must open an attachment this is sent in an e-mail message and then click through a series of Content Advisor setup windows.

Do not open or save content rating files (.rat files) that you receive from untrusted sources.

This vulnerability could be exploited when a user installs a .rat file. Do not open files that use this file name extension.

Help prevent e-mail attacks by blocking content rating files (.rat files).

This vulnerability could be exploited when a user installs a .rat file. To help block these files by using Outlook and Outlook Express, see Microsoft Knowledge Base Article 837388 and Microsoft Knowledge Base Article 291387. Enterprise customers could consider adding content rating files (.rat files) to the list of unsafe files that are blocked by enterprise gateway e-mail filters.

Set Internet and Local intranet security zone settings to “High” to prompt before running 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 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:

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.

Alternatively, you can change your settings to prompt before running Active Scripting only. To do this, follow these steps:

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. Prompting before running Active Scripting 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 Active Scripting. 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 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:

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.

Install the update that is described in Microsoft Security Bulletin MS04-018 if you are using Outlook Express 5.5 SP2.

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.

Customers who use one or more of these products could be at a reduced risk from an e-mail-borne attack that tries to exploit this vulnerability unless the user clicks a malicious link in the e-mail message.

Read e-mail messages in plain text format if you are using 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: