Microsoft Posts Advisory About New Internet Explorer Vulnerability
A new security vulnerability has been posted by Microsoft that could allow an attacker to execute code remotely on the affected computer system. Affected are Internet Explorer 6 to Internet Explorer 8 on pretty much every client and server operating system since - and including - Windows XP. Microsoft explains that "the vulnerability exists due to the creation of uninitialized memory during a CSS function within Internet Explorer" and that it is "possible under certain conditions for the memory to be leveraged by an attacker using a specially crafted Web page to gain remote code execution".
Mitigating factors help in limiting the impact of the vulnerability on target systems. Microsoft mentions protected mode, a feature of Internet Explorer on Windows Vista and later Windows operating system. Protected Mode gives the attacker limited rights on the affected system.
The other mitigating factors are:
- 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. See also Managing Internet Explorer Enhanced Security Configuration.
- 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, reducing 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.
- An attacker who successfully exploits 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.
- 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.