Internet Explorer Vulnerabity Allows Remote Code

[From Microsoft Security Advisory (2458511): Vulnerability in Internet Explorer Could Allow Remote Code Execution - full page includes suggested action, workarounds]

Microsoft Security Advisory (2458511)

Vulnerability in Internet Explorer Could Allow Remote Code Execution

Published: November 03, 2010 | Updated: November 03, 2010

Version: 1.1

General Information

Executive Summary

Microsoft is investigating new, public reports of a vulnerability in all supported versions of Internet Explorer. The main impact of the vulnerability is remote code execution. This advisory contains workarounds and mitigations for this issue.

The vulnerability exists due to an invalid flag reference within Internet Explorer. It is possible under certain conditions for the invalid flag reference 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:
• Data Execution Prevention (DEP) helps protect against attacks that result in code execution and is enabled by default in Internet Explorer 8 on the following Windows operating systems: Windows XP Service Pack 3, Windows Vista Service Pack 1, Windows Vista Service Pack 2, and Windows 7.

• 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 7 or Internet Explorer 8 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 attacker’s Web site.

• By default, all supported versions of Microsoft Outlook, Microsoft Outlook Express, and Windows Mail open HTML e-mail messages in the Restricted sites zone, which disables script and ActiveX controls, removing the risk of an attacker being able to use this vulnerability to execute malicious code. 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.

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Frequently Asked Questions

What is the scope of the advisory?
Microsoft is aware of a new vulnerability that affects Internet Explorer 6, Internet Explorer 7, and Internet Explorer 8.

Is this a security vulnerability that requires Microsoft to issue a security update?
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.

How could an attacker exploit this vulnerability?
An attacker could host a specially crafted Web site that is designed to exploit this vulnerability through Internet Explorer and then convince a user to view the Web site. The attacker could also take advantage of compromised Web sites and Web sites that accept or host user-provided content or advertisements. These Web sites 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 in an Instant Messenger message that takes users to the attacker's Web site.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could gain the same user rights as the logged-on user. If the user is logged on with administrative user rights, an attacker who successfully exploited this vulnerability 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.

What is Data Execution Prevention (DEP)?
Data Execution Prevention support is included in Internet Explorer, and although on by default for Internet Explorer 8, is off by default for earlier versions of Internet Explorer. DEP is designed to help foil attacks by preventing code from running in memory that is marked non-executable. For more information about DEP in Internet Explorer, please see the MSDN blog post, IE8 Security Part I: DEP/NX Memory Protection.

There are multiple ways to enable DEP for IE on a system. You can enable DEP manually for IE (see also Microsoft Knowledge Base Article 875352), use an automated Microsoft Fix it solution to enable DEP for IE7, or use Enhanced Mitigation Experience Toolkit v2.0 to enable DEP automatically for applications that are configured in EMET. These methods are detailed in the following Workaround section.

What is the Enhanced Mitigation Experience Toolkit v2.0 (EMET)?
The Enhanced Mitigation Experience Toolkit (EMET) is a utility that helps prevent vulnerabilities in software from being successfully exploited. EMET achieves this by using security mitigation technologies. These technologies function as special protections and obstacles that an exploit author must defeat in order to exploit software vulnerabilities. These security mitigation technologies do not guarantee that vulnerabilities cannot be exploited, but work to make exploitation as difficult to accomplish as possible. In many instances, a fully functional exploit that can bypass EMET may never be developed. For more information, see Microsoft Knowledge Base Article 2458544.

[From Microsoft Security Advisory (2458511): Vulnerability in Internet Explorer Could Allow Remote Code Execution - full page includes suggested action, workarounds]

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