Microsoft Security Bulletin MS15-079 - Critical

Cumulative Security Update for Internet Explorer (3082442)

Published: August 11, 2015

Version: 1.0

Executive Summary

This security update resolves vulnerabilities in Internet Explorer. The most severe of the vulnerabilities could allow remote code execution if a user views a specially crafted webpage using Internet Explorer. An attacker who successfully exploited these vulnerabilities could gain the same user rights as the current user. Customers whose accounts are configured to have fewer user rights on the system could be less impacted than those who operate with administrative user rights.

This security update is rated Critical for Internet Explorer 7 (IE 7), Internet Explorer 8 (IE 8), Internet Explorer 9 (IE 9), Internet Explorer 10 (IE 10), and Internet Explorer 11 (IE 11) on affected Windows clients, and Moderate for Internet Explorer 7 (IE 7), Internet Explorer 8 (IE 8), Internet Explorer 9 (IE 9), Internet Explorer 10 (IE 10), and Internet Explorer 11 (IE 11) on affected Windows servers. For more information, see the Affected Software section.

The security update addresses the vulnerabilities by:

• Modifying how Internet Explorer handles objects in memory
• Helping to ensure that affected versions of Internet Explorer properly implement the ASLR security feature
• Helping to improve command-line parameters for Notepad execution from Internet Explorer

For more information about the vulnerabilities, see the Vulnerability Information section.

For more information about this update, see Microsoft Knowledge Base Article 3082442.

Affected Software

The following software versions or editions are affected. Versions or editions that are not listed are either past their support life cycle or are not affected. To determine the support life cycle for your software version or edition, see Microsoft Support Lifecycle.

Affected Software 

^[1]This update is available via Windows Update.

^[2]The Windows 10 update is cumulative. In addition to containing non-security updates, it also contains all of the security fixes for all of the Windows 10-affected vulnerabilities shipping with this month’s security release. The update is available via the Windows Update Catalog only. See Microsoft Knowledge Base Article 3081436 for more information and download links.

*The Updates Replaced column shows only the latest update in any chain of superseded updates. For a comprehensive list of updates replaced, go to the Microsoft Update Catalog, search for the update KB number, and then view update details (updates replaced information is provided on the Package Details tab).

Note Windows Server Technical Preview 2 is affected. Customers running this operating system are encouraged to apply the update, which is available via Windows Update.

Severity Ratings and Vulnerability Identifiers

The following severity ratings assume the potential maximum impact of the vulnerability. For information regarding the likelihood, within 30 days of this security bulletin's release, of the exploitability of the vulnerability in relation to its severity rating and security impact, please see the Exploitability Index in the August bulletin summary.

Where specified in the Severity Ratings and Impact table, Critical, Important, and Moderate values indicate severity ratings. For more information, see Security Bulletin Severity Rating System. Refer to the following key for the abbreviations used in the table to indicate maximum impact:

Update FAQ

CVE-2015-2423 discussed in this bulletin is also discussed in other bulletins being released in August. Do I need to install multiple updates to be protected from this vulnerability?

Yes. To be protected from CVE-2015-2423, customers must apply all of the updates provided in this bulletin for their affected software, as well as the update for Microsoft Office provided in MS15-081. Likewise, customers running an affected version of Microsoft Windows must also install the applicable updates provided in MS15-088. Customers who do not install all of the updates available for their affected software will not be fully protected from the vulnerability.

Vulnerability Information

Multiple Memory Corruption Vulnerabilities

Remote code execution vulnerabilities exist when Internet Explorer improperly accesses objects in memory. These vulnerabilities could corrupt memory in such a way that an attacker could execute arbitrary code in the context of the current user.

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 by adding 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 instant messenger or email 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. 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. Systems where Internet Explorer is used frequently, such as workstations or terminal servers, are at the most risk from these vulnerabilities.

The update addresses the vulnerabilities by modifying how Internet Explorer handles objects in memory. The following table contains links to the standard entry for each vulnerability in the Common Vulnerabilities and Exposures list:

Mitigating Factors

Microsoft has not identified any mitigating factors for these vulnerabilities.

Workarounds

Microsoft has not identified any workarounds for these vulnerabilities.

FAQ

I am running Internet Explorer on Windows Server 2008, Windows Server 2008 R2, Windows Server 2012, or Windows Server 2012 R2. Does this mitigate these vulnerabilities? 
Yes. By default, Internet Explorer on Windows Server 2008, Windows Server 2008 R2, Windows Server 2012, and Windows Server 2012 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.

Can EMET help mitigate attacks that attempt to exploit these vulnerabilities? 
Yes. The Enhanced Mitigation Experience Toolkit (EMET) enables users to manage security mitigation technologies that help make it more difficult for attackers to exploit memory corruption vulnerabilities in a given piece of software. EMET can help mitigate attacks that attempt to exploit these vulnerabilities in Internet Explorer on systems where EMET is installed and configured to work with Internet Explorer.

For more information about EMET, see the Enhanced Mitigation Experience Toolkit.

Multiple ASLR Bypass Vulnerabilities

Security feature bypass vulnerabilities exist when Internet Explorer fails to use the Address Space Layout Randomization (ASLR) security feature, allowing an attacker to more reliably predict the memory offsets of specific instructions in a given call stack. An attacker who successfully exploited this vulnerability could bypass the Address Space Layout Randomization (ASLR) security feature, which helps protect users from a broad class of vulnerabilities. The security feature bypass by itself does not allow arbitrary code execution. However, an attacker could use this ASLR bypass vulnerability in conjunction with another vulnerability, such as a remote code execution vulnerability, to more reliably run arbitrary code on a target system.

In a web-browsing scenario, successful exploitation of these vulnerabilities requires that a user is logged on and running an affected version of Internet Explorer, and browses to a malicious site. 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.

The update addresses these vulnerabilities by helping to ensure that affected versions of Internet Explorer properly implement the ASLR security feature. The following table contains links to the standard entry for each vulnerability in the Common Vulnerabilities and Exposures list:

Mitigating Factors

Microsoft has not identified any mitigating factors for this vulnerability.

Workarounds

Microsoft has not identified any workarounds for this vulnerability.

Unsafe Command Line Parameter Passing Vulnerability - CVE-2015-2423

An information disclosure vulnerability exists in Microsoft Windows, Internet Explorer, and Microsoft Office when files at a medium integrity level become accessible to Internet Explorer running in Enhanced Protection Mode (EPM).

To exploit this vulnerability, an attacker would first need to leverage another vulnerability and execute code in Internet Explorer with EPM, and then execute Excel, Notepad, PowerPoint, Visio, or Word using an unsafe command line parameter. The update addresses the vulnerability by improving how Notepad and Microsoft Office programs are executed from Internet Explorer.

Important To be protected from this vulnerability, customers must apply the updates provided in this bulletin, as well as Windows updates provided in MS15-088. Likewise, customers running an affected Microsoft Office product must also apply the applicable updates provided in MS15-081. Customers who do not install all of the updates available for their affected software will not be fully protected from the vulnerability.

The following table contains links to the standard entry for each vulnerability in the Common Vulnerabilities and Exposures list:

Mitigating Factors

Microsoft has not identified any mitigating factors for this vulnerability.

Workarounds

The following workarounds may be helpful in your situation:

• Remove notepad.exe from Internet Explorer elevation policy

  Note Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or view the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe.

  1. Run regedit.exe.
  2. In Registry Editor, expand the following registry key:
     "HKEY_LOCAL_MACHINE\Software\Microsoft\Internet Explorer\Low Rights\ElevationPolicy"
  3. Select {dc6bf185-7ae4-444e-8c35-e447b0d2bd1e}, click File, and then click Export.
  4. In the Export Registry File dialog, enter notepad.exe_backup.reg, and then click Save.
  5. Click File, select Delete, and then click Yes.
  6. Log off and log on again, or restart the computer.  

  Impact of workaround: Internet Explorer will be disallowed from executing Notepad with elevated privileges.

  How to undo the workaround.

  1. Run regedit.exe.
  2. In Registry Editor, click File, and then click Import.
  3. In the Import Registry File dialog, select the backup file that you created in the initial procedure, notepad.exe_backup.reg, and then click Open.
  4. Log off and log on again, or restart the computer.

• Remove the IE elevation policies for Word, Excel, PowerPoint, and Visio

  Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

  1. Click Start, click Run, type Regedit in the Open box, and then click OK.
  2. Navigate to the following registry location:
     HKEY_LOCAL_MACHINE\Software\Microsoft\Internet Explorer\Low Rights\ElevationPolicy
  3. For each of the following subkeys, perform the steps that follow:
  4. {000209FF-0000-0000-C000-000000000046}
  5. {2BBE903C-2776-4574-9855-EC1597ABE3D6}
  6. {63F463ED-322A-4DE8-8E6F-65DD293F7461}
  7. {FC88B53C-9B2A-1A25-5867-C8612E79DBF6}
     1. Select the subkey.
     2. Click the File menu and then click Export.
     3. In the Export Registry File dialog box, type <a unique file name> and then click Save.
        Note This will create a backup of this registry key in the My Documents folder by default.
     4. Click the File menu and then select Delete.
     5. Click Yes.
     6. Log all users off and on again, or then restart the computer.

How to undo the workaround

1. Click Start, click Run, type Regedit in the Open box, and then click OK.
2. Navigate to the following registry location:
   HKEY_LOCAL_MACHINE\Software\Microsoft\Internet Explorer\Low Rights\ElevationPolicy
3. For each of the four .reg files, perform the following steps:
   1. Click the File menu and then select Import.
   2. In the Import Registry File dialog box, select the appropriate file and then click Open.
   3. Exit the Registry Editor.
   4. Restart the computer.

FAQ

I am running Internet Explorer for Windows Server 2008, Windows Server 2008 R2, Windows Server 2012, or Windows Server 2012 R2. Does this mitigate this vulnerability? 
Yes. By default, Internet Explorer on Windows Server 2008, Windows Server 2008 R2, Windows Server 2012, and Windows Server 2012 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.

Security Update Deployment

For Security Update Deployment information see the Microsoft Knowledge Base article referenced in the Executive Summary.

Acknowledgments

Microsoft recognizes the efforts of those in the security community who help us protect customers through coordinated vulnerability disclosure. See Acknowledgments for more information.

Disclaimer

The information provided in the Microsoft Knowledge Base is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

Revisions

• V1.0 (August 11, 2015): Bulletin published.

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