Microsoft Security Bulletin MS15-043 - Critical

• 10/11/2017
• 26 minutes to read
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Cumulative Security Update for Internet Explorer (3049563)

Published: May 12, 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 6 (IE 6), 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 6 (IE 6), 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 JScript and VBScript and Internet Explorer properly implement the ASLR security feature
• Adding additional permission validations to Internet Explorer
• Helping to prevent information stored in a user’s clipboard from being accessed by a malicious site

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

For more information about this update, see Microsoft Knowledge Base Article 3049563.

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 

Note Windows Technical Preview and Windows Server Technical Preview are affected. Customers running these operating systems are encouraged to apply the update, which is available via Windows Update. 

Update FAQ

For addressing CVE-2015-1684 and CVE-2015-1686, what updates apply to my system?
CVE-2015-1684 is a vulnerability in the VBScript engine and CVE-2015-1686 is a vulnerability in the JScript and VBScript engines. Although the attack vector is through Internet Explorer, the vulnerabilities are addressed by this update (3049563) only for systems running Internet Explorer 8, Internet Explorer 9, Internet Explorer 10, and Internet Explorer 11. For Internet Explorer 7 and earlier and for systems without Internet Explorer installed, the vulnerabilities are addressed by the update described in MS15-053.

The update that addresses CVE-2015-1684 and CVE-2015-1686 depends on the version of the JScript and VBScript scripting engines that are installed on your system. Consult the following table for update information.

Does this update contain any additional security-related changes to functionality?
In addition to the changes that are listed for the vulnerabilities described in this bulletin, this update includes defense-in-depth updates to help improve security-related features.

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 May 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:

^[1]Internet Explorer 7 installed on Windows Server 2003 is not affected by this vulnerability.

Vulnerability Information

VBScript ASLR Bypass - CVE-2015-1684

A security feature bypass exists when the VBScript engine 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. The security feature bypass by itself does not allow arbitrary code execution. However, an attacker could use the ASLR bypass in conjunction with another vulnerability, such as a remote code execution vulnerability, that could take advantage of the ASLR bypass to more reliably run arbitrary code on a target system.

In a web-browsing scenario, successful exploitation of an ASLR bypass requires that a user is logged on and running an affected version of Internet Explorer, and browses to a malicious website. Therefore, any systems where a web browser is used frequently, such as workstations or terminal servers, are at the most risk from ASLR bypasses. 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 this ASLR bypass by helping to ensure that affected versions of VBScript 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:

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

VBScript and JScript ASLR Bypass - CVE-2015-1686

A security feature bypass exists when the JScript and VBScript engines fail 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. The security feature bypass by itself does not allow arbitrary code execution. However, an attacker could use the ASLR bypass 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 an ASLR bypass 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 ASLR bypasses. 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 this ASLR bypasses by helping to ensure that affected versions of JScript and VBScript 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: