Microsoft Security Bulletin MS13-021 - 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-based attack scenario, an attacker could host a specially crafted website that is designed to exploit these vulnerabilities through Internet Explorer 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 these vulnerabilities. In all cases, however, an attacker would have no way to force users to view the attacker-controlled content. Instead, an attacker would have to convince users to take action, 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, or by getting them to open an attachment sent through email.
• An attacker who successfully exploited these vulnerabilities could gain the same user rights as the current 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, all supported versions of Microsoft Outlook, Microsoft Outlook Express, and Windows Mail open HTML email messages in the Restricted sites zone. The Restricted sites zone, which disables script and ActiveX controls, helps reduce the risk of an attacker being able to use these vulnerabilities to execute malicious code. If a user clicks a link in an email message, the user could still be vulnerable to exploitation of these vulnerabilities through the web-based attack scenario.
• By default, Internet Explorer on Windows Server 2003, Windows Server 2008, Windows Server 2008 R2, and Windows Server 2012 runs in a restricted mode that is known as Enhanced Security Configuration. This mode mitigates these vulnerabilities. See the FAQ section for these vulnerabilities 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:

• Set Internet and Local intranet security zone settings to "High" to block ActiveX Controls and Active Scripting in these zones

  You can help protect against exploitation of these vulnerabilities by changing your settings for the Internet security zone to block ActiveX controls and Active Scripting. You can do this by setting your browser security to High.

  To raise the browsing security level in Internet Explorer, perform the following 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 Internet.
  3. Under Security level for this zone, move the slider to High. This sets the security level for all websites you visit to High.
  4. Click Local intranet.
  5. Under Security level for this zone, move the slider to High. This sets the security level for all websites you visit to High.
  6. Click OK to accept the changes and return to Internet Explorer.

  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 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 even with the security setting set to High.

  Impact of workaround. There are side effects to blocking ActiveX Controls and Active Scripting. Many websites that are on the Internet or on an intranet use ActiveX or Active Scripting to provide additional functionality. For example, an online e-commerce site or banking site may use ActiveX Controls to provide menus, ordering forms, or even account statements. Blocking ActiveX Controls or Active Scripting is a global setting that affects all Internet and intranet sites. If you do not want to block ActiveX Controls or Active Scripting for such sites, use the steps outlined in "Add sites that you trust to the Internet Explorer Trusted sites zone".

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

  After you set Internet Explorer to block ActiveX controls and Active Scripting in the Internet zone and in the Local intranet zone, you can add sites that you trust to the Internet Explorer Trusted sites zone. This will allow you to continue to use trusted websites exactly as you do today, while helping to protect yourself from this attack on untrusted sites. We recommend that you add only sites that you trust to the Trusted sites zone.

  To do this, 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 website to the zone box, type the URL of a site that you trust, and then click Add.
  5. Repeat these steps for each site that you want to add to the zone.
  6. Click OK two times to accept the changes and return to Internet Explorer.

  Note Add any sites that you trust not to take malicious action on your system. Two in particular that you may want to add are *.windowsupdate.microsoft.com and *.update.microsoft.com. These are the sites that will host the update, and it requires an ActiveX Control to install the update.

   

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

  You can help protect against exploitation of these vulnerabilities by changing your settings to prompt before running Active Scripting or to disable Active Scripting in the Internet and Local intranet security zone. To do this, perform the following steps:

  1. In Internet Explorer, click Internet Options on the Tools menu.
  2. Click the Security tab.
  3. Click Internet, and then click Custom Level.
  4. Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK.
  5. Click Local intranet, and then click Custom Level.
  6. Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK.
  7. Click OK two times to return to Internet Explorer.

  Note Disabling Active Scripting in the Internet and Local intranet security zones may cause some 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.

  Impact of workaround. There are side effects to prompting before running Active Scripting. Many websites that are on the Internet or on an intranet use Active Scripting to provide additional functionality. For example, an online e-commerce site or banking site may use Active Scripting to provide menus, ordering forms, or even account statements. Prompting before running Active Scripting is a global setting that affects all Internet and intranet sites. You will be prompted frequently when you enable this workaround. For each prompt, if you feel you trust the site that you are visiting, click Yes to run Active Scripting. If you do not want to be prompted for all these sites, use the steps outlined in "Add sites that you trust to the Internet Explorer Trusted sites zone".

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

  After you set Internet Explorer to require a prompt before it runs ActiveX controls and Active Scripting in the Internet zone and in the Local intranet zone, you can add sites that you trust to the Internet Explorer Trusted sites zone. This will allow you to continue to use trusted 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 website 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.

What is the scope of the vulnerabilities? 
These are remote code execution vulnerabilities in the context of the current user.

What causes the vulnerabilities? 
When Internet Explorer attempts to access an object in memory that has been deleted, it may corrupt memory in such a way that an attacker could execute arbitrary code in the context of the current user.

What might an attacker use the vulnerabilities to do? 
An attacker who successfully exploited these vulnerabilities could gain the same user rights as the current user. If the current user is logged on with administrative user rights, an attacker who successfully exploited these vulnerabilities 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.

How could an attacker exploit the vulnerabilities? 
An attacker could host a specially crafted website that is designed to exploit these vulnerabilities through Internet Explorer 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 these vulnerabilities. In all cases, however, an attacker would have no way to force users to view the attacker-controlled content. Instead, an attacker would have to convince users to take action, 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, or by getting them to open an attachment sent through email.

What systems are primarily at risk from the vulnerabilities? 
Systems where Internet Explorer is used frequently, such as workstations or terminal servers, are at the most risk from these vulnerabilities.

I am running Internet Explorer for Windows Server 2003, Windows Server 2008, Windows Server 2008 R2, or Windows Server 2012. Does this mitigate these vulnerabilities? 
Yes. By default, Internet Explorer on Windows Server 2003, Windows Server 2008, Windows Server 2008 R2, and Windows Server 2012 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 is the Enhanced Mitigation Experience Toolkit v3.0 (EMET)? 
The Enhanced Mitigation Experience Toolkit (EMET) is a utility that helps prevent vulnerabilities in software from being successfully exploited. EMET achieves this by using security mitigation technologies. These technologies function as special protections and obstacles that an exploit author must defeat in order to exploit software vulnerabilities. These security mitigation technologies do not guarantee that vulnerabilities cannot be exploited, but work to make exploitation as difficult to accomplish as possible. In many instances, a fully functional exploit that can bypass EMET may never be developed. For more information, see Microsoft Knowledge Base Article 2458544.

Does EMET help mitigate attacks that try to exploit these vulnerabilities? 
Yes. The Enhanced Mitigation Experience Toolkit (EMET) helps mitigate the exploitation of these vulnerabilities by adding additional protection layers that make the vulnerabilities harder to exploit. EMET is a utility that helps prevent vulnerabilities in software from being successfully exploited for code execution, by applying the latest security mitigation technologies. At this time, EMET is provided with limited support and is only available in the English language. For more information, see Microsoft Knowledge Base Article 2458544.

What does the update do? 
The update addresses the vulnerabilities by modifying the way that Internet Explorer handles objects in memory.

When this security bulletin was issued, had these vulnerabilities been publicly disclosed? 
Consult the following table:

When this security bulletin was issued, had Microsoft received any reports that these vulnerabilities are being exploited? 
No. Microsoft had not received any information to indicate that these vulnerabilities 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.

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.

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.

Reference Table

The following table contains the security update information for this software.

Reference Table

The following table contains the security update information for this software.

Reference Table

The following table contains the security update information for this software.

Reference Table

The following table contains the security update information for this software.

Reference Table

The following table contains the security update information for this software.

Reference Table

The following table contains the security update information for this software.