Microsoft Security Bulletin MS15-125 - Critical

Cumulative Security Update for Microsoft Edge (3116184)

Published: December 8, 2015 | Updated: December 16, 2015

Version: 1.1

Executive Summary

This security update resolves vulnerabilities in Microsoft Edge. The most severe of the vulnerabilities could allow remote code execution if a user views a specially crafted webpage using Microsoft Edge. An attacker who successfully exploited the 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 Microsoft Edge on Windows 10. For more information, see the Affected Software section.

The update addresses the vulnerabilities by:

• Modifying how Microsoft Edge handles objects in memory
• Helping to ensure that Microsoft Edge properly enforces content types
• Helping to ensure that Microsoft Edge properly handles exceptions when dispatching certain window messages
• Correcting how Microsoft Edge parses HTTP responses
• Adding permission validations to Microsoft Edge
• Preventing the XSS filter in Microsoft Edge from incorrectly disabling HTML attributes

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

For more information about this update, see Microsoft Knowledge Base Article 3116184.

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]Windows 10 updates are cumulative. In addition to containing non-security updates, they also contain all of the security fixes for all of the Windows 10-affected vulnerabilities shipping with the monthly security release. The updates are available via the Microsoft Update Catalog.

Note Windows Server Technical Preview 3 and Windows Server Technical Preview 4 are affected. Customers running these operating systems 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 December 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 Microsoft Edge Memory Corruption Vulnerabilities

Multiple remote code execution vulnerabilities exist when Microsoft Edge improperly accesses objects in memory. The 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 the vulnerabilities through Microsoft Edge, 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 the 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 way of enticement in an email or Instant Messenger message, or by getting them to open an attachment sent through email.

An attacker who successfully exploited the 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 the 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. The update addresses the vulnerabilities by modifying how Microsoft Edge 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.

Microsoft Browser Elevation of Privilege Vulnerability - CVE-2015-6139

An elevation of privilege vulnerability exists when Microsoft Edge does not properly enforce content types. An attacker who successfully exploited the vulnerability could run arbitrary script 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 this vulnerability could elevate privileges in affected versions of Microsoft Edge.

The update addresses the vulnerability by helping to ensure that Microsoft Edge properly enforces content types. Microsoft received information about this vulnerability through coordinated vulnerability disclosure. At the time this security bulletin was originally issued, Microsoft was unaware of any attack attempting to exploit this vulnerability.

Mitigating Factors

Microsoft has not identified any mitigating factors for this vulnerability.

Workarounds

Microsoft has not identified any workarounds for this vulnerability.

Microsoft Browser ASLR Bypass - CVE-2015-6161

A security feature bypass for Microsoft Edge exists as a result of how exceptions are handled when dispatching certain window messages, allowing an attacker to probe the layout of the address space and thereby bypassing Address Space Layout Randomization (ASLR). By itself, the ASLR bypass does not allow arbitrary code execution. However, an attacker could use this ASLR bypass in conjunction with another vulnerability, such as a remote code execution vulnerability, to run arbitrary code on a target system. Successful exploitation of the ASLR bypass requires a user to be logged on and running an affected version of Microsoft Edge. The user would then need to browse to a malicious site.

The update addresses the ASLR bypass by helping to ensure that Microsoft Edge properly handles exceptions when dispatching certain window messages.

Microsoft received information about this bypass through coordinated disclosure. At the time this security bulletin was originally issued, Microsoft was unaware of any attack attempting to exploit this bypass.

Mitigating Factors

Microsoft has not identified any mitigating factors for this vulnerability.

Workarounds

Microsoft has not identified any workarounds for this vulnerability.

Microsoft Edge Spoofing Vulnerability - CVE-2015-6169

A spoofing vulnerability exists when Microsoft Edge does not properly parse HTTP responses. An attacker who successfully exploited this vulnerability could trick a user by redirecting them to a specially crafted website. The specially crafted website could spoof content or be used as a pivot to chain an attack with other vulnerabilities in web services.

To exploit the vulnerability, the user must click a specially crafted URL. In an email attack scenario, an attacker could send an email message containing the specially crafted URL to the user in an attempt to convince the user to click it.

In a web-based attack scenario, an attacker could host a specially crafted website designed to appear as a legitimate website to the user. However, the attacker would have no way to force the user to visit the specially crafted website. The attacker would have to convince the user to visit the specially crafted website, typically by way of enticement in an email or Instant Messenger message, and then convince the user to interact with content on the website.

The update addresses the vulnerability by correcting how Microsoft Edge parses HTTP responses. Microsoft received information about this vulnerability through coordinated vulnerability disclosure. At the time this security bulletin was originally issued, Microsoft was unaware of any attack attempting to exploit this vulnerability.

Mitigating Factors

Microsoft has not identified any mitigating factors for this vulnerability.

Workarounds

Microsoft has not identified any workarounds for this vulnerability.

Microsoft Browser Elevation of Privilege Vulnerability - CVE-2015-6170

An elevation of privilege vulnerability exists when Microsoft Edge does not properly validate permissions under specific conditions, potentially allowing 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 this vulnerability could elevate privileges in affected editions of Microsoft Edge.

The update addresses the vulnerabilities by adding permission validations to Microsoft Edge. Microsoft received information about this vulnerability through coordinated vulnerability disclosure. At the time this security bulletin was originally issued, Microsoft was unaware of any attack attempting to exploit this vulnerability.

Mitigating Factors

Microsoft has not identified any mitigating factors for this vulnerability.

Workarounds

Microsoft has not identified any workarounds for this vulnerability.

Microsoft Edge XSS Filter Bypass Vulnerability - CVE-2015-6176

An XSS filter bypass vulnerability exists in the way that Microsoft Edge disables an HTML attribute in otherwise appropriately filtered HTTP response data. The vulnerability could allow initially disabled scripts to run in the wrong security context, leading to information disclosure.

An attacker could post on a website specially crafted content that is designed to exploit the vulnerability. The attacker would then have to convince the user to view the content on the affected website. If the user then browses to the website, the XSS filter disables HTML attributes in the specially crafted content, creating a condition that could allow malicious script to run in the wrong security context, leading to information disclosure.

An attacker who successfully exploited the vulnerability could cause script to run on another user's system in the guise of a third-party website. Such script would run inside the browser when visiting the third-party website, and could take any action on the user's system that the third-party website was permitted to take. The vulnerability could only be exploited if the user clicked a hypertext link, either in an HTML email or if the user visited an attacker's website or a website containing content that is under the attacker’s control.

The update addresses the vulnerability by preventing the XSS filter in Microsoft Edge from incorrectly disabling HTML attributes. Microsoft received information about this vulnerability through coordinated disclosure. At the time this security bulletin was originally issued, Microsoft was unaware of any attack attempting to exploit this vulnerability.

Mitigating Factors

Microsoft has not identified any mitigating factors for this vulnerability.

Workarounds

Microsoft has not identified any workarounds for this vulnerability.

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 (December 8, 2015): Bulletin published.
• V1.1 (December 16, 2015): Revised the vulnerability description for CVE-2015-6161 to more accurately describe the ASLR Bypass. This is an informational change only. Customers who have already successfully installed security update 3116869 or 3116900 do not need to take any action.

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