Cumulative Security Update for Internet Explorer (MS05-020)
13 Apr. 2005
Summary
A remote code execution vulnerability exists in Internet Explorer because of the way that it handles certain DHTML objects, certain URLs and Content Advisory files. An attacker could exploit these vulnerabilities by constructing a malicious Web page. This malicious Web page could potentially allow remote code execution if a user visited a malicious Web site.
Affected Software:
* Microsoft Windows 2000 Service Pack 3 and Microsoft Windows 2000 Service Pack 4
* Microsoft Windows XP Service Pack 1 and Microsoft Windows XP Service Pack 2
* Microsoft Windows XP 64-Bit Edition Service Pack 1 (Itanium)
* Microsoft Windows XP 64-Bit Edition Version 2003 (Itanium)
* Microsoft Windows Server 2003
* Microsoft Windows Server 2003 for Itanium-based Systems
* Microsoft Windows 98, Microsoft Windows 98 Second Edition (SE), and * Microsoft Windows Millennium Edition (ME) Tested Microsoft Windows Components:
Affected Components:
* Internet Explorer 5.01 Service Pack 3 on Microsoft Windows 2000 Service Pack 3: Download the update
* Internet Explorer 5.01 Service Pack 4 on Microsoft Windows 2000 Service Pack 4: Download the update
* Internet Explorer 5.5 Service Pack 2 on Microsoft Windows Millennium Edition Review the FAQ section of this bulletin for details about this version.
* Internet Explorer 6 Service Pack 1 on Microsoft Windows 2000 Service Pack 3, on Microsoft Windows 2000 Service Pack 4, or on Microsoft Windows XP Service Pack 1: Download the update
* Internet Explorer 6 Service Pack 1 on Microsoft Windows 98, on Microsoft Windows 98 SE, or on Microsoft Windows Millennium Edition Review the FAQ section of this bulletin for details about this version.
* Internet Explorer 6 Service Pack 1 for Microsoft Windows XP 64-Bit Edition Service Pack 1 (Itanium): Download the update
* Internet Explorer 6 for Microsoft Windows Server 2003: Download the update
* Internet Explorer 6 for Microsoft Windows Server 2003 for Itanium-based Systems and Microsoft Windows XP 64-Bit Edition Version 2003 (Itanium): Download the update
* Internet Explorer 6 for Microsoft Windows XP Service Pack 2: Download the update
Non-Affected Software:
* Microsoft Windows Server 2003 Service Pack 1
* Microsoft Windows Server 2003 with SP1 for Itanium-based Systems
* Microsoft Windows Server 2003 x64 Edition
* Microsoft Windows XP Professional x64 Edition
DHTML Object Memory Corruption Vulnerability - CAN-2005-0553:
A remote code execution vulnerability exists in Internet Explorer because of the way that it handles certain DHTML objects. An attacker could exploit the vulnerability by constructing a malicious Web page. This malicious Web page could allow remote code execution if a user visited a malicious Web site. An attacker who successfully exploited this vulnerability could take complete control of an affected system.
DHTML Object Memory Corruption Vulnerability - CAN-2005-0553
A remote code execution vulnerability exists in Internet Explorer because of the way that it handles certain DHTML objects. An attacker could exploit the vulnerability by constructing a malicious Web page. This malicious Web page could allow remote code execution if a user visited a malicious Web site. An attacker who successfully exploited this vulnerability could take complete control of an affected system.
Mitigating Factors for DHTML Object Memory Corruption Vulnerability - CAN-2005-0553:
* 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:
* Apply the update that is included with Microsoft Security Bulletin MS03-040 or a later Cumulative Security Update for Internet Explorer.
* Use Microsoft Outlook Express 6 or a later version in its default configuration.
* Use Microsoft Outlook 2000 Service Pack 2 or a later version in its default configuration.
* 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.
Workarounds for DHTML Object Memory Corruption Vulnerability - CAN-2005-0553:
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 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:
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. 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:
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, 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.
7. Click OK two times to return to Internet Explorer.
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:
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.
* 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.
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.
FAQ for DHTML Object Memory Corruption Vulnerability - CAN-2005-0553:
What is the scope of the vulnerability?
This is a remote code execution 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?
A race condition could occur in Internet Explorer when it processes DHTML objects.
What are DHTML objects?
The Dynamic HTML (DHTML) object model allows for more dynamic content on Web pages than HTML. For more information about DHTML, see the product documentation.
What is a race condition?
A race condition is typically associated with synchronization errors that provide a window of opportunity during which one process can interfere with another potentially introducing a remote code execution vulnerability. Race conditions may for example occur as a result of the relative timing of events in multithreaded operating systems and software. Race conditions are frequently difficult to exploit in predictable ways. For more information about race conditions, see the MSDN Library Web site.
Why does this race condition cause a vulnerability?
This race condition could create an environment where a series of specially timed requests could cause the Internet Explorer to perform an unpredictable action. However, because the circumstances that lead to this condition could change every time that the vulnerability is exploited, it may be difficult for an attacker to exploit this vulnerability.
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 on the system, or could cause malicious code to run in the security context of the locally logged on user. 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.
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 users 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.
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 on the Advanced tab in the Internet Options dialog box. Some of the important modifications include the following:
* 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.
What does the update do?
The update removes the vulnerability by modifying the way Internet Explorer synchronizes the threads that are being used to process the specially crafted messages.
When this security bulletin was issued, had this vulnerability been publicly disclosed?
No. Microsoft received information about this vulnerability through responsible disclosure.
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.
URL Parsing Memory Corruption Vulnerability - CAN-2005-0554
A remote code execution vulnerability exists in Internet Explorer because of the way that it handles certain URLs. An attacker could exploit the vulnerability by constructing a malicious Web page. This malicious Web page could potentially allow remote code execution if a user visited a malicious Web site. An attacker who successfully exploited this vulnerability could take complete control of an affected system.
Mitigating Factors for URL Parsing Memory Corruption Vulnerability - CAN-2005-0554:
* 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:
* Apply the update that is included with Microsoft Security Bulletin MS03-040 or a later Cumulative Security Update for Internet Explorer.
* Use Microsoft Outlook Express 6 or a later version in its default configuration.
* Use Microsoft Outlook 2000 Service Pack 2 or a later version in its default configuration.
* 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.
Workarounds for URL Parsing Memory Corruption Vulnerability - CAN-2005-0554:
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 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:
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.
Alternatively, you can change your settings to prompt before running Active Scripting 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 Scripting section, under Active Scripting, click Prompt, 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.
7. Click OK two times to return to Internet Explorer.
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:
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.
* 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 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.
FAQ for URL Parsing Memory Corruption Vulnerability - CAN-2005-0554: What is the scope of the vulnerability?
This is a remote code execution 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?
The process used by Internet Explorer to validate the buffer used when it processes certain URLs.
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 on the system, or could cause malicious code to run in the security context of the locally logged on user. 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.
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 users 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.
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?
No. Microsoft received information about this vulnerability through responsible disclosure.
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.
Content Advisor Memory Corruption Vulnerability - CAN-2005-0555
A remote code execution vulnerability exists in Internet Explorer because of the way that it handles Content Advisor files. An attacker could exploit the vulnerability by constructing a specially crafted Content Advisor file. This malicious Content Advisor file could potentially allow remote code execution if a user visited a malicious Web site or viewed a malicious e-mail message and accepted the installation of the file. An attacker who successfully exploited this vulnerability could take complete control of an affected system. However, significant user interaction is required to exploit this vulnerability.
Mitigating Factors for Content Advisor Memory Corruption Vulnerability - CAN-2005-0555:
* 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:
* Apply the update that is included with Microsoft Security Bulletin MS03-040 or a later Cumulative Security Update for Internet Explorer.
* Use Microsoft Outlook Express 6 or a later version in its default configuration.
* Use Microsoft Outlook 2000 Service Pack 2 or a later version in its default configuration.
* 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.
FAQ for Content Advisor Memory Corruption Vulnerability - CAN-2005-0555: What is the scope of the vulnerability?
This is a remote code execution 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?
The process used by Internet Explorer to validate the buffer used when it processes certain Content Advisor content.
What is the Internet Explorer Content Advisor?
Internet Explorer Content Advisor allows you to rate the appropriateness of Web content and to control which Web sites your users can visit. This feature is intended to be used to define a more secure environment that help protect your users from content on the Internet that is not appropriate. For more information about the Content Advisor, see the product documentation.
Microsoft IIS Web server administrators can rate content in support of the Internet Explorer Content Advisor on a Web site by using content ratings. For more information about content ratings, see the product documentation.
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 on the system, or could cause malicious code to run in the security context of the locally logged on user. A user would then have to click through a series of Content Advisor setup windows for an attack to be successful.
An attacker could also send a content ratings file (.rat) in e-mail and persuade a user to install it. A user would have to click through a series of Content Advisor setup windows for an attack to be successful.
If the content ratings file on an IIS Web server has been replaced with a malicious content ratings file, an attacker could cause code execution on the Web server. However, the Web server would already have been compromised because the file resides in an area where, by default, only Administrators have write access. This update also addresses this vector.
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 users 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.
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?
No. Microsoft received information about this vulnerability through responsible disclosure.
