Microsoft Security Bulletin MS15-094 - Critical

• 10/11/2017
• 19 minutes to read
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Cumulative Security Update for Internet Explorer (3089548)

Published: September 8, 2015 | Updated: December 13, 2016

Version: 1.1

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:

1. Modifying how Internet Explorer handles objects in memory
2. Modifying how Internet Explorer, JScript, and VBScript handle objects in memory
3. Helping to ensure that Internet Explorer correctly permits file operations

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

For more information about this update, see Microsoft Knowledge Base Article 3089548.

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 

^[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. See Microsoft Knowledge Base Article 3081444 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*The Updates Replaced column shows only the latest update in any chain of superseded updates.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 and Windows Server Technical Preview 3 are 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 September 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:

 Vulnerability Information

Multiple Memory Corruption Vulnerabilities in Internet Explorer

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 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:

• For 32-bit systems, enter the following command at an administrative command prompt:

takeown /f %windir%\system32\vbscript.dll   
cacls %windir%\system32\vbscript.dll /E /P everyone:N  
cacls %windir%\system32\jscript.dll /E /P everyone:N

• For 64-bit systems, enter the following command at an administrative command prompt:

takeown /f %windir%\syswow64\vbscript.dll   
cacls %windir%\syswow64\vbscript.dll /E /P everyone:N  
cacls %windir%\syswow64\jscript.dll /E /P everyone:N

Impact of Workaround. Websites that use VBScript or JScript may not work properly.

How to undo the workaround.

• For 32-bit systems, enter the following command at an administrative command prompt:

cacls %windir%\system32\vbscript.dll /E /R everyone  
cacls %windir%\system32\jscript.dll /E /R everyone

• For 64-bit systems, enter the following command at an administrative command prompt:

cacls %windir%\syswow64\vbscript.dll /E /R everyone  
cacls %windir%\syswow64\jscript.dll /E /R everyone

Elevation of Privilege Vulnerability – CVE-2015-2489

An elevation of privilege vulnerability exists when Internet Explorer does not properly validate permissions under specific conditions, potentially allowing a script to be run with elevated privileges.

In a web-based attack scenario, an attacker could host a website 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, 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. For example, an attacker could trick users into clicking a link that takes them to the attacker's site. An attacker who successfully exploited the vulnerability could elevate privileges in affected versions of Internet Explorer.

The vulnerability by itself does not allow arbitrary code to be run. However, the vulnerability could be used in conjunction with another vulnerability (e.g., a remote code execution vulnerability) that could take advantage of the elevated privileges when running arbitrary code. For example, an attacker could exploit another vulnerability to run arbitrary code through Internet Explorer, but due to the context in which processes are launched by Internet Explorer, the code might be restricted to run at a low integrity level (very limited permissions). However, an attacker could, in turn, exploit the vulnerability to cause the arbitrary code to run at a medium integrity level (permissions of the current user).

The update addresses the vulnerability by adding additional permission validations to Internet Explorer. The following table contains links to the standard entry for the vulnerability in the Common Vulnerabilities and Exposures list: