MS Warns of IE/XP Server Exploit

Stephen Yagielowicz
A speaker at the recent Blackhat DC security conference, Jorge Luis Alvarez Medina of Core Security Technologies, demonstrated a previously undocumented method of remotely turning a Windows XP-based computer into a web server — thus exposing the hacked computer's file system to the public. As surprising to the audience as the apparent ease with which this attack was performed, was the news that instead of being a patchable exploit, the attack may actually be enabled by a design feature of the Internet Explorer browser software.

For its part, Microsoft issued Security Advisory 980088, entitled "Vulnerability in Internet Explorer Could Allow Information Disclosure," which detailed the problem and its recommended remedies:

"Microsoft is investigating a publicly reported vulnerability in Internet Explorer for customers running Windows XP or who have disabled Internet Explorer Protected Mode," the report reads. "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."

"In a web-based attack scenario, an attacker could host a website that contains a web page that is used to exploit this vulnerability," the report states. "In addition, compromised websites and websites 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 websites," the report continued. "Instead, an attacker would have to convince users to visit the website, typically by getting them to click a link in an email message or Instant Messenger message that takes users to the attacker's website."

The advisory warns that an attacker who successfully exploited this vulnerability could gain the same user rights as the local user; and that while users whose accounts are configured to have fewer rights on the system could be less affected than those operating with administrative user rights, many systems remain vulnerable.

"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," the report said. "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."

According to the company, affected versions include 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. Other, older versions of the Internet Explorer software are also vulnerable.

Microsoft says that running Internet Explorer in Protected Mode prevents exploitation of this vulnerability. This is the default setting for Internet Explorer on Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008.

The company also plans to take the appropriate action to protect its customers, which may include providing a solution through its 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," a company spokesperson stated. "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."

As for standard security precautions, Microsoft advises customers to enable a firewall, apply all software updates and install antivirus and antispyware software.