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             AUSCERT External Security Bulletin Redistribution

                              ESB-2010.0233.2
   Vulnerability in Internet Explorer Could Allow Remote Code Execution
                               10 March 2010

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        AusCERT Security Bulletin Summary
        ---------------------------------

Product:           Internet Explorer 6
                   Internet Explorer 7
Publisher:         Microsoft
Operating System:  Windows 2000
                   Windows XP
                   Windows Vista
                   Windows Server 2003
                   Windows Server 2008
Impact/Access:     Execute Arbitrary Code/Commands -- Remote with User Interaction
Resolution:        Mitigation
CVE Names:         CVE-2010-0806  

Original Bulletin: 
   http://www.microsoft.com/technet/security/advisory/981374.mspx

Comment: Microsoft is aware that this vulnerability is currently being used
         in targeted attacks.

Revision History:  March 10 2010: Updated to reflect this vulnerability requires user interaction
                   March 10 2010: Initial Release

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Microsoft Security Advisory (981374)

Vulnerability in Internet Explorer Could Allow Remote Code Execution

Published: March 09, 2010

Version: 1.0

General Information

Executive Summary

  Microsoft is investigating new, public reports of a vulnerability in
  Internet Explorer 6 and Internet Explorer 7. Our investigation has shown that
  the latest version of the browser, Internet Explorer 8, is not affected. The
  main impact of the vulnerability is remote code execution. This advisory
  contains information about which versions of Internet Explorer are vulnerable
  as well as workarounds and mitigations for this issue.

  Our investigation so far has shown that Internet Explorer 8 and Internet 
  Explorer 5.01 Service Pack 4 on Microsoft Windows 2000 Service Pack 4 are not
  affected, and that Internet Explorer 6 Service Pack 1 on Microsoft Windows 
  2000 Service Pack 4, and Internet Explorer 6 and Internet Explorer 7 are 
  vulnerable.

  The vulnerability exists due to an invalid pointer reference being used
  within Internet Explorer. It is possible under certain conditions for the
  invalid pointer to be accessed after an object is deleted. In a
  specially-crafted attack, in attempting to access a freed object, Internet
  Explorer can be caused to allow remote code execution.

  At this time, we are aware of targeted attacks attempting to use this 
  vulnerability. We will continue to monitor the threat environment and update 
  this advisory if this situation changes. On completion of this investigation,
  Microsoft will take the appropriate action to protect our customers, which
  may include providing a solution through our monthly security update release 
  process, or an out-of-cycle security update, depending on customer needs.

  We are actively working with partners in our Microsoft Active Protections 
  Program (MAPP) and our Microsoft Security Response Alliance (MSRA) programs
  to provide information that they can use to provide broader protections to 
  customers. In addition, we are actively working with partners to monitor the 
  threat landscape and take action against malicious sites that attempt to 
  exploit this vulnerability.

  Microsoft continues to encourage customers to follow the "Protect Your 
  Computer" guidance of enabling a firewall, applying all software updates and 
  installing anti-virus and anti-spyware software. Additional information can
  be found at Security at home.

Mitigating Factors:

  Internet Explorer 8 is not affected by this vulnerability.

  Protected Mode in Internet Explorer on Windows Vista and later Windows 
  operating systems helps to limit the impact of the vulnerability as an 
  attacker who successfully exploited this vulnerability would have very
  limited rights on the system. An attacker who successfully exploited this 
  vulnerability on Internet Explorer 6 or Internet Explorer 7 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 affected than users who 
  operate with administrative user rights.

  In a Web-based attack scenario, an attacker could host a Web site that 
  contains a Web page that is used to exploit this vulnerability. In addition, 
  compromised Web sites and Web sites 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 Web sites. Instead, an attacker would have to 
  convince users to visit the Web site, typically by getting them to click a 
  link in an e-mail message or Instant Messenger message that takes users to
  the attackers Web site.

  By default, Internet Explorer on Windows Server 2003 and Windows Server 2008 
  runs in a restricted mode that is known as Enhanced Security Configuration. 
  This mode sets the security level for the Internet zone to High. This is a 
  mitigating factor for Web sites that you have not added to the Internet 
  Explorer Trusted sites zone.

  By default, all supported versions of Microsoft Outlook, Microsoft Outlook 
  Express, and Windows Mail open HTML e-mail messages in the Restricted sites 
  zone, removing the risk of an attacker being able to use this vulnerability
  to execute malicious code. The Restricted sites zone helps mitigate attacks
  that could try to exploit this vulnerability by preventing Active Scripting
  and ActiveX controls from being used when reading HTML e-mail messages.
  However, if a user clicks a link in an e-mail message, the user could still
  be vulnerable to exploitation of this vulnerability through the Web-based
  attack scenario. Additionally, Outlook 2007 uses a different component to
  render HTML e-mail, removing the risk of this exploit.

Affected Software

  Microsoft Windows 2000 Service Pack 4
  Windows XP Service Pack 2 and Windows XP Service Pack 3
  Windows XP Professional x64 Edition Service Pack 2
  Windows Server 2003 Service Pack 2
  Windows Server 2003 x64 Edition Service Pack 2
  Windows Server 2003 with SP2 for Itanium-based Systems
  Windows Vista, Windows Vista Service Pack 1, and Windows Vista Service Pack 2
  Windows Vista x64 Edition , Windows Vista x64 Edition Service Pack 1, and
    Windows Vista x64 Edition and Service Pack 2
  Windows Server 2008 for 32-bit Systems and Windows Server 2008 for 32-bit
    Systems Service Pack 2
  Windows Server 2008 for x64-based Systems and Windows Server 2008 for x64-based
    Systems Service Pack 2
  Windows Server 2008 for Itanium-based Systems and Windows Server 2008 for
    Itanium-based Systems Service Pack 2
  Internet Explorer 6 Service Pack 1 on Microsoft Windows 2000 Service Pack 4
  Internet Explorer 6 for Windows XP Service Pack 2, Windows XP Service Pack 3,
    and Windows XP Professional x64 Edition Service Pack 2
  Internet Explorer 6 for Windows Server 2003 Service Pack 2, Windows Server
    2003 with SP2 for Itanium-based Systems, and Windows Server 2003 x64 Edition
    Service Pack 2
  Internet Explorer 7 for Windows XP Service Pack 2, Windows XP Service Pack 3,
    and Windows XP Professional x64 Edition Service Pack 2
  Internet Explorer 7 for Windows Server 2003 Service Pack 2, Windows Server
    2003 with SP2 for Itanium-based Systems, and Windows Server 2003 x64
    Edition Service Pack 2
  Internet Explorer 7 in Windows Vista, Windows Vista Service Pack 1, Windows
    Vista Service Pack 2, Windows Vista x64 Edition, Windows Vista x64 Edition
    Service Pack 1, and Windows Vista x64 Edition Service Pack 2
  Internet Explorer 7 in Windows Server 2008 for 32-bit Systems and Windows
    Server 2008 for 32-bit Systems Service Pack 2
  Internet Explorer 7 in Windows Server 2008 for Itanium-based Systems and
    Windows Server 2008 for Itanium-based Systems Service Pack 2
  Internet Explorer 7 in Windows Server 2008 for x64-based Systems and Windows
    Server 2008 for x64-based Systems Service Pack 2

Workarounds

  Microsoft has tested the following workarounds. Although 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.

Modify the Access Control List (ACL) on iepeers.dll

  To modify the ACL on iepeers.dll to be more restrictive, run the following 
  commands from a command prompt with administrative privileges:

  For 32-bit Windows Systems:

    Echo y| cacls %WINDIR%\SYSTEM32\iepeers.DLL /E /P everyone:N

  For x64-based Windows Systems:

    Echo y| cacls %WINDIR%\SYSWOW64\iepeers.DLL /E /P everyone:N

  Impact of workaround. Extended MSHTML functionality such as printing and Web 
  folders may be affected.

  How to undo the workaround.

  Run the following commands from a command prompt with administrative 
  privileges:

  For 32-bit Windows Systems:

    cacls %WINDIR%\SYSTEM32\iepeers.dll /E /R everyone

  For x64-based Windows Systems:

    cacls %WINDIR%\SYSWOW64\iepeers.dll /E /R everyone

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 prompt before running
  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, 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 
  security setting set to High.

  Impact of workaround. There are side effects to blocking ActiveX Controls and
  Active Scripting. Many Web sites 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 ActiveX Controls and Active Scripting to be
  blocked 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 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.

  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, 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 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 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.

  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. 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".

Enable DEP for Internet Explorer 6 Service Pack 2 or Internet Explorer 7

   This vulnerability is more difficult to exploit successfully if Data
  Execution Prevention (DEP) is enabled for Internet Explorer. You can enable
  DEP for all versions of Internet Explorer that support DEP, using one of the
  following 
  methods:

Enable DEP for Internet Explorer 7 interactively

  Local Administrators can control DEP/NX by running Internet Explorer as an 
  Administrator. To enable DEP, perform the following steps:

  1. In Internet Explorer, click Tools, click Internet Options, and then
     click Advanced.

  2. Click Enable memory protection to help mitigate online attacks.

Enable DEP for Internet Explorer using automated Microsoft Fix It

  See Microsoft Knowledge Base Article 981374 to use the automated Microsoft
  Fix it solution to enable or disable this workaround.

  Impact of workaround. Some browser extensions may not be compatible with
  DEP and may exit unexpectedly. If this occurs, you can disable the add-on,
  or revert the DEP setting using the Internet Control Panel. This is also 
  accessible using the System Control panel.

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