Microsoft Security Bulletin MS12-035 - Critical

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:

• In a web browsing attack scenario, an attacker could host a website that contains a webpage that is used to exploit this vulnerability. In addition, compromised websites and websites that accept or host user-provided content or advertisements could contain specially crafted content that could exploit this vulnerability. In all cases, however, an attacker would have no way to force users to visit these websites. Instead, an attacker would have to convince users to visit the website, typically by getting them to click a link in an email message or Instant Messenger message that takes users to the attacker's website.
• 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 only on Windows Server 2008 and Windows Server 2008 R2, and only in a web browsing attack scenario. See the FAQ section of this vulnerability for more information about Internet Explorer Enhanced Security Configuration.
• Standard .NET Framework applications are not affected by this vulnerability. Only specially crafted .NET Framework applications could exploit this vulnerability.

Workaround refers to a setting or configuration change that does not correct the underlying vulnerability but would help block known attack vectors before you apply the update. Microsoft has tested the following workarounds and states in the discussion whether a workaround reduces functionality:

• Disable partially trusted Microsoft .NET applications

  To disable all Microsoft .NET applications running at partial trust, including XAML browser applications (XBAPs) and Microsoft .NET applications located on the network, run the following commands from an elevated command prompt:

  caspol –pp off
caspol –m –resetlockdown
caspol –pp on

  Note You must be logged in as administrator or have administrative credentials to complete this workaround.

  Impact of workaround. Microsoft .NET applications may not run.

  How to undo the workaround.

  To reset the Microsoft .NET security policies to the defaults, run the following commands from an elevated command prompt:

  caspol –pp off
caspol –m –reset
caspol –pp on

  Note You must be logged in as administrator or have administrative credentials to undo this workaround.

• Disable XAML browser applications in Internet Explorer

  To help protect against this vulnerability, change your settings to prompt before running XAML browser applications (XBAPs) or to disable XBAPs in the Internet and Local intranet security zones as follows:

  1. In Internet Explorer, click the Tools menu and then select Internet Options.
  2. Click the Security tab, click Internet, and then click Custom level. Under Settings, for Loose XAML, click Prompt or Disable, and then click OK.
  3. Click the Security tab, click Internet, and then click Custom level. Under Settings, for XAML browser applications, click Prompt or Disable, and then click OK.
  4. Click the Security tab, click Internet, and then click Custom level. Under Settings, for XPS documents, click Prompt or Disable, and then click OK.
  5. On the Security tab, click Custom level. Under .NET Framework-reliant components, set Run components not signed with Authenticode to either Prompt or Disable, and then click OK. Repeat this step for Run components signed with Authenticode, and then click OK.
  6. Click Local intranet, and then click Custom Level. Repeat steps 3 and 4. If you are prompted to confirm that you want to change these settings, click Yes. Click OK to return to Internet Explorer.

  Impact of workaround. Microsoft .NET code will not run in Internet Explorer or will not run without prompting. Disabling Microsoft .NET applications and components in the Internet and Local intranet security zones may cause some websites to work incorrectly. If you have difficulty using a website 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.

  Add sites that you trust to the Internet Explorer Trusted sites zone

  After you set Internet Explorer to disable XAML browser applications or require a prompt before it runs Loose XAML, XAML browser applications, or XPS documents 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 websites 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, perform the following 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.

  How to undo the workaround. Perform the following steps:

  1. In Internet Explorer, click the Tools menu, and then select Internet Options.
  2. Click the Security tab, click Reset all zones to default level, and then click OK.

What is the scope of the vulnerability? 
This is a remote code execution vulnerability. 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.

What causes the vulnerability? 
This vulnerability is caused when the serialization process within the .NET Framework incorrectly treats untrusted data as trusted.

What is Serialization in the .NET Framework? 
Serialization is the process of converting the state of an object into a form that can be persisted or transported. The complement of serialization is deserialization, which converts a stream into an object. The most basic serializer in the .NET Framework in the binary serializer. For more information about this component, see the MSDN article Binary Serialization.

What might an attacker use the vulnerability to do? 
An attacker who successfully exploited this vulnerability could run arbitrary code as the logged-on user. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. If a user is logged-on with administrative user rights, an attacker could take complete control of the affected system. 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.

How could an attacker exploit the vulnerability? 
There are two attack scenarios possible for exploiting this vulnerability: a web browsing scenario and a Windows .NET application bypass of Code Access Security (CAS) restrictions. These scenarios are described as follows:

• Web browsing attack scenario
  An attacker could host a specially crafted website that contains a specially crafted XBAP (XAML browser application) that could exploit this vulnerability and then convince a user to view the website. The attacker could also take advantage of compromised websites and websites that accept or host user-provided content or advertisements. These websites could contain specially crafted content that could exploit this vulnerability. In all cases, however, an attacker would have no way to force users to visit these websites. Instead, an attacker would have to convince users to visit the website, typically by getting them to click a link in an email message or in an Instant Messenger message that takes users to the attacker's website. It could also be possible to display specially crafted web content by using banner advertisements or by using other methods to deliver web content to affected systems.
• Windows .NET applications attack scenario
  This vulnerability could also be used by Windows .NET applications to bypass Code Access Security (CAS) restrictions.

What is an XAML Browser Application (XBAP)? 
An XAML browser application (XBAP) combines features of both a web application and a rich-client application. Like web applications, XBAPs can be published to a web server and launched from Internet Explorer. Like rich-client applications, XBAPs can take advantage of the capabilities of Windows Presentation Foundation (WPF). For more information about XBAPs, see MSDN article, Windows Presentation Foundation XAML Browser Applications Overview.

What are .NET Framework Code Access Security (CAS) Restrictions? 
The .NET Framework provides a security mechanism called code access security to help protect computer systems from malicious mobile code, to allow code from unknown origins to run with protection, and to help prevent trusted code from intentionally or accidentally compromising security. Code access security (CAS) enables code to be trusted to varying degrees depending on where the code originates and on other aspects of the code's identity. Code access security also enforces the varying levels of trust on code, which minimizes the amount of code that must be fully trusted in order to run. Using code access security can reduce the likelihood that your code will be misused by malicious or error-filled code. For more information on CAS, see the MSDN article, Code Access Security.

What systems are primarily at risk from the vulnerability? 
There are two types of systems at risk from this vulnerability, described as follows: systems that are using the web browsing scenario and systems that are using the Windows .NET applications scenario.

• Web browsing scenario
  Successful exploitation of this vulnerability requires that a user is logged on and is visiting websites using a web browser capable of instantiating XBAPs. Therefore, any systems where a web browser is used frequently, such as workstations or terminal servers, are at the most risk from this vulnerability. Servers could be at more risk if administrators allow users to browse and read email on servers. However, best practices strongly discourage allowing this.
• Windows .NET applications
  Workstations and servers that run untrusted Windows .NET applications are also at risk from this vulnerability.

I am running Internet Explorer for Windows Server 2003, Windows Server 2008, or Windows Server 2008 R2. Does this mitigate this vulnerability? 
Yes. 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. Enhanced Security Configuration is a group of preconfigured settings in Internet Explorer that can reduce the likelihood of a user or administrator downloading and running specially crafted web content on a server. This is a mitigating factor for websites that you have not added to the Internet Explorer Trusted sites zone.

What does the update do? 
The update addresses the vulnerability by correcting the manner in which the .NET Framework serialization process handles trusted and untrusted data.

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

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:

• In a web browsing attack scenario, an attacker could host a website that contains a webpage that is used to exploit this vulnerability. In addition, compromised websites and websites that accept or host user-provided content or advertisements could contain specially crafted content that could exploit this vulnerability. In all cases, however, an attacker would have no way to force users to visit these websites. Instead, an attacker would have to convince users to visit the website, typically by getting them to click a link in an email message or Instant Messenger message that takes users to the attacker's website.
• 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 only on Windows Server 2008 and Windows Server 2008 R2, and only in a web browsing attack scenario. See the FAQ section of this vulnerability for more information about Internet Explorer Enhanced Security Configuration.

Workaround refers to a setting or configuration change that does not correct the underlying vulnerability but would help block known attack vectors before you apply the update. Microsoft has tested the following workarounds and states in the discussion whether a workaround reduces functionality:

• Disable XAML browser applications in Internet Explorer

  To help protect against this vulnerability, change your settings to prompt before running XAML browser applications (XBAPs) or to disable XBAPs in the Internet and Local intranet security zones as follows:

  1. In Internet Explorer, click the Tools menu and then select Internet Options.
  2. Click the Security tab, click Internet, and then click Custom level. Under Settings, for Loose XAML, click Prompt or Disable, and then click OK.
  3. Click the Security tab, click Internet, and then click Custom level. Under Settings, for XAML browser applications, click Prompt or Disable, and then click OK.
  4. Click the Security tab, click Internet, and then click Custom level. Under Settings, for XPS documents, click Prompt or Disable, and then click OK.
  5. On the Security tab, click Custom level. Under .NET Framework-reliant components, set Run components not signed with Authenticode to either Prompt or Disable, and then click OK. Repeat this step for Run components signed with Authenticode, and then click OK.
  6. Click Local intranet, and then click Custom Level. Repeat steps 3 and 4. If you are prompted to confirm that you want to change these settings, click Yes. Click OK to return to Internet Explorer.

  Impact of workaround. Microsoft .NET code will not run in Internet Explorer or will not run without prompting. Disabling Microsoft .NET applications and components in the Internet and Local intranet security zones may cause some websites to work incorrectly. If you have difficulty using a website 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.

  Add sites that you trust to the Internet Explorer Trusted sites zone

  After you set Internet Explorer to disable XAML browser applications or require a prompt before it runs Loose XAML, XAML browser applications, or XPS documents 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 websites 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, perform the following 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.

  How to undo the workaround. Perform the following steps:

  1. In Internet Explorer, click the Tools menu, and then select Internet Options.
  2. Click the Security tab, click Reset all zones to default level, and then click OK.

What is the scope of the vulnerability? 
This is a remote code execution vulnerability. 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.

What causes the vulnerability? 
The vulnerability is caused when the .NET Framework improperly handles an exception during the object serialization process.

What is Object Serialization in the .NET Framework? 
Serialization can be defined as the process of storing the state of an object instance to a storage medium. During this process, the public and private fields of the object and the name of the class, including the assembly containing the class, is converted to a stream of bytes, which is then written to a data stream. When the object is subsequently deserialized, an exact clone of the original object is created. For more information, see the MSDN article Object Serialization in the .NET Framework.

What might an attacker use the vulnerability to do? 
In the web browsing scenario, an attacker who successfully exploited this vulnerability could obtain the same permissions as the currently logged-on user. If a user is logged on with administrative user rights, an attacker could take complete control of the 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.

How could an attacker exploit the vulnerability? 
There are two attack scenarios possible for exploiting this vulnerability: a web browsing scenario and a Windows .NET application bypass of Code Access Security (CAS) restrictions. These scenarios are described as follows:

• Web browsing attack scenario
  An attacker could host a specially crafted website that contains a specially crafted XBAP (XAML browser application) that could exploit this vulnerability and then convince a user to view the website. The attacker could also take advantage of compromised websites and websites that accept or host user-provided content or advertisements. These websites could contain specially crafted content that could exploit this vulnerability. In all cases, however, an attacker would have no way to force users to visit these websites. Instead, an attacker would have to convince users to visit the website, typically by getting them to click a link in an email message or in an Instant Messenger message that takes users to the attacker's website. It could also be possible to display specially crafted web content by using banner advertisements or by using other methods to deliver web content to affected systems.
• Windows .NET applications attack scenario
  This vulnerability could also be used by Windows .NET applications to bypass Code Access Security (CAS) restrictions.

What is an XAML Browser Application (XBAP)? 
An XAML browser application (XBAP) combines features of both a web application and a rich-client application. Like web applications, XBAPs can be published to a web server and launched from Internet Explorer. Like rich-client applications, XBAPs can take advantage of the capabilities of Windows Presentation Foundation (WPF). For more information about XBAPs, see MSDN article, Windows Presentation Foundation XAML Browser Applications Overview.

What are .NET Framework Code Access Security (CAS) Restrictions? 
The .NET Framework provides a security mechanism called code access security to help protect computer systems from malicious mobile code, to allow code from unknown origins to run with protection, and to help prevent trusted code from intentionally or accidentally compromising security. Code access security (CAS) enables code to be trusted to varying degrees depending on where the code originates and on other aspects of the code's identity. Code access security also enforces the varying levels of trust on code, which minimizes the amount of code that must be fully trusted in order to run. Using code access security can reduce the likelihood that your code will be misused by malicious or error-filled code. For more information on CAS, see the MSDN article, Code Access Security.

What systems are primarily at risk from the vulnerability? 
There are two types of systems at risk from this vulnerability, described as follows: systems that are using the web browsing scenario and systems that are using the Windows .NET applications scenario.

• Web browsing scenario
  Successful exploitation of this vulnerability requires that a user is logged on and is visiting websites using a web browser capable of instantiating XBAPs. Therefore, any systems where a web browser is used frequently, such as workstations or terminal servers, are at the most risk from this vulnerability. Servers could be at more risk if administrators allow users to browse and read email on servers. However, best practices strongly discourage allowing this.
• Windows .NET applications
  Workstations and servers that run untrusted Windows .NET applications are also at risk from this vulnerability.

I am running Internet Explorer for Windows Server 2003, Windows Server 2008, or Windows Server 2008 R2. Does this mitigate this vulnerability? 
Yes. 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. Enhanced Security Configuration is a group of preconfigured settings in Internet Explorer that can reduce the likelihood of a user or administrator downloading and running specially crafted web content on a server. This is a mitigating factor for websites that you have not added to the Internet Explorer Trusted sites zone.

What does the update do? 
The update addresses the vulnerability by correcting the manner in which the Microsoft .NET Framework handles object serialization.

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

Reference Table

The following table contains the security update information for this software. You can find additional information in the subsection, Deployment Information, in this section.

Note The update for supported versions of Windows XP Professional x64 Edition also applies to supported versions of Windows Server 2003 x64 Edition.

Reference Table

The following table contains the security update information for this software. You can find additional information in the subsection, Deployment Information, in this section.

Note The update for supported versions of Windows Server 2003 x64 Edition also applies to supported versions of Windows XP Professional x64 Edition.

Reference Table

The following table contains the security update information for this software. You can find additional information in the subsection, Deployment Information, in this section.

Reference Table

The following table contains the security update information for this software. You can find additional information in the subsection, Deployment Information, in this section.

Reference Table

The following table contains the security update information for this software. You can find additional information in the subsection, Deployment Information, in this section.

Reference Table

The following table contains the security update information for this software. You can find additional information in the subsection, Deployment Information, in this section.