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Microsoft Security Advisory (980088)

Vulnerability in Internet Explorer Could Allow Information Disclosure

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Microsoft is investigating a publicly reported vulnerability in Internet Explorer for customers running Windows XP or who have disabled Internet Explorer Protected Mode. This advisory contains information about which versions of Internet Explorer are vulnerable as well as workarounds and mitigations for this issue.

Our investigation so far has shown that if a user is using a version of Internet Explorer that is not running in Protected Mode an attacker may be able to access files with an already known filename and location. These versions include Internet Explorer 5.01 Service Pack 4 on Microsoft Windows 2000 Service 4; Internet Explorer 6 Service Pack 1 on Microsoft Windows 2000 Service Pack 4; and Internet Explorer 6, Internet Explorer 7, and Internet Explorer 8 on supported editions of Windows XP Service Pack 2, Windows XP Service Pack 3, and Windows Server 2003 Service Pack 2. Protected Mode prevents exploitation of this vulnerability and is running by default for versions of Internet Explorer on Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008.

The vulnerability exists due to content being forced to render incorrectly from local files in such a way that information can be exposed to malicious websites.

Microsoft has released MS10-035 to address the known vector for the main issue in Internet Explorer 7 and Internet Explorer 8, which are the newer versions of Internet Explorer. However, all versions of Internet Explorer remain subject to an issue that, if an attacker is able to cache content in a predictable location on a user's system, and is able to determine the user name, then the attacker may be able to view files on the local system to which the user has access.

At this time, we are unaware of any 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:

  • Protected Mode prevents exploitation of this vulnerability and is running by default for supported versions of Internet Explorer on Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008 R2.
  • 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.
  • An attacker who successfully exploited this vulnerability 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.
  • By default, Internet Explorer on Windows Server 2003 and Windows Server 2008 runs in a restricted mode that is known as Enhanced Security Configuration. This mode sets the security level for the Internet zone to High. This is a mitigating factor for Web sites that you have not added to the Internet Explorer Trusted sites zone.
  • By default, all supported versions of Microsoft Outlook, Microsoft Outlook Express, and Windows Mail open HTML e-mail messages in the Restricted sites zone. The Restricted sites zone helps mitigate attacks that could try to exploit this vulnerability by preventing Active Scripting and ActiveX controls from being used when reading HTML e-mail messages. However, 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.

General Information

Overview

Frequently Asked Questions

Suggested Actions

Other Information

Resources:

Disclaimer:

The information provided in this advisory 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 (February 3, 2010): Advisory published.
  • V1.1 (February 10, 2010): Specified the mitigation offered by Protected Mode. Also clarified an FAQ and workaround pertaining to Protected Mode.
  • V1.2 (June 9, 2010): Added information about MS10-035 and clarified a FAQ entry about the caching vector.