Microsoft Security Bulletin MS13-020 - 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 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 them to the attacker's website.
• 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.

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:

• Do not open Microsoft Office and WordPad documents from untrusted sources

  Do not open Microsoft Office or Rich Text Format (.rtf) files that you receive from untrusted sources or that you receive unexpectedly from trusted sources. This vulnerability could be exploited when a user opens a specially crafted file.

• Prevent ActiveX controls from running in Office 2007 and Office 2010

  To disable ActiveX controls in Microsoft Office 2007 and Microsoft Office 2010, perform the following steps:

  1. Click File, click Options, click Trust Center, and then click Trust Center Settings.
  2. Click ActiveX Settings in the left-hand pane, and then select Disable all controls without notifications.
  3. Click OK to save your settings.

  Impact of workaround. Office documents that use embedded ActiveX controls may not display as intended.

  How to undo the workaround. 

  To re-enable ActiveX controls in Microsoft Office 2007 and Microsoft Office 2010, perform the following steps:

  1. Click File, click Options, click Trust Center, and then click Trust Center Settings.
  2. Click ActiveX Settings in the left-hand pane, and then deselect Disable all controls without notifications.
  3. Click OK to save your settings.
• 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 this vulnerability 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 this vulnerability 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.

• Use Microsoft Office File Block policy to block the opening of RTF documents from unknown or untrusted sources and locations

  Note Modifying the Registry incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from incorrect modification of the Registry can be solved. Modify the Registry at your own risk.

  For Office 2003 

  The following registry scripts can be used to set the File Block policy.

  Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Word\Security\FileOpenBlock]
"RtfFiles"=dword:00000001

  Note In order to use 'FileOpenBlock' with Microsoft Office 2003, all of the latest security updates for Microsoft Office 2003 must be applied.

  For Office 2007 

  The following registry scripts can be used to set the File Block policy.

  Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.0\Word\Security\FileOpenBlock]
"RtfFiles"=dword:00000001

  Note In order to use 'FileOpenBlock' with Microsoft Office 2007, all of the latest security updates for Microsoft Office 2007 must be applied.

  For Microsoft Office 2010

  1. Open Word 2010 and follow the steps below:
  2. Click the File tab.
  3. Under Help, click Options.
  4. Click Trust Center, and then click Trust Center Settings.
  5. In the Trust Center, click File Block Settings.
  6. Ensure that the Open checkbox is selected for the following file types:
     - RTF Files
  7. Under Open behavior for selected file types, select Do not open selected file types or select Open selected file types in Protected View. Either choice will block the attack vector to the vulnerable code.
  8. Click OK to apply the File Block Settings.

  Alternatively, file block can be applied using Group Policy. For more information, see the TechNet article, Plan file block settings for Office 2010.

  Impact of workaround. For Microsoft Office 2003 and Microsoft Office 2007, users who have configured the File Block policy and have not configured a special exempt directory or have not moved files to a trusted location will be unable to open Office 2003 files or earlier versions. For Microsoft Office 2010, Office 2003 files or earlier versions will either be blocked from opening or will be opened in protected mode depending on the open behavior that was selected. For more information about the impact of file block setting in Microsoft Office software, see Microsoft Knowledge Base Article 922850.

  How to undo the workaround.

  For Office 2003

  Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Word\Security\FileOpenBlock]
"RtfFiles"=dword:00000000

  For Office 2007

  Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.0\Word\Security\FileOpenBlock]
"RtfFiles"=dword:00000000

  For Microsoft Office 2010, open Microsoft Word 2010 and perform the following steps:

  1. Click the File tab.
  2. Under Help, click Options.
  3. Click Trust Center, and then click Trust Center Settings.
  4. In the Trust Center, click File Block Settings.
  5. Clear the Open check box for the file types that you previously selected.
  6. Click OK to apply the File Block settings.

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

What causes the vulnerability? 
The vulnerability is caused by the way that OLE Automation parses a specially crafted file.

What is OLE Automation? 
Object Linking and Embedding (OLE) Automation is a Windows protocol that allows an application to share data with or to control another application. OLE Automation is an industry standard that applications use to expose their OLE objects to development tools, macro languages, and other containers that support OLE Automation.

What might an attacker use the vulnerability to do? 
If a user is logged on with administrative user rights, an attacker who successfully exploited this vulnerability 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? 
This vulnerability requires that a user of an affected version of Microsoft Windows open a specially crafted RTF file.

In an email attack scenario, an attacker could exploit the vulnerability by sending specially-crafted RTF-formatted data in the contents of an email message. The vulnerability could be exploited when the specially crafted RTF email message is opened in Outlook while using Microsoft Word as the email viewer. An attacker could also exploit the vulnerability by sending a specially-crafted RTF file as an attachment and convincing the user to open the specially crafted RTF file.

In a web-based attack scenario, an attacker could host a website that contains a file that is used to attempt to exploit this vulnerability. In addition, compromised websites and websites that accept or host user-provided content could contain specially crafted content that could exploit this vulnerability. In all cases, an attacker would have no way to force users to visit a specially crafted website. Instead, an attacker would have to convince them to visit the website, typically by getting them to click a link that takes them to the attacker's site, and then convince them to open the specially crafted file.

What systems are primarily at risk from the vulnerability? 
Workstations running Windows XP Service Pack 3 are primarily at risk from this vulnerability.

What does the update do? 
This security update addresses the vulnerability by correcting the manner in which OLE Automation parses files.

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.