Another URL-Handling Bug Hits IE

A mere two days after Patch Tuesday brought a host of remote-code execution vulnerabilities to light, Microsoft issued a security advisory warning of yet another problem: a URL-handling vulnerability that could lead to systems getting hijacked if running Internet Explorer 7 on Windows XP or Windows 2003.

Mark Miller, director of security response communication, said in a statement Oct. 10 that the Redmond, Wash., company is working on a security update.

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Miller said that a successful exploit of the flaw would entail a user clicking on a rigged link from an e-mail message and thereby downloading arbitrary code that could take over the victims system.

A proliferation of URI-handling bugs is making it all a little confusing, but Microsoft told eWEEK that the advisory issued on Oct. 10 is not for the protocol handler issue that got attention in early July. "For clarification, back in June, a number of issues were discussed publicly that involved potential vulnerabilities in protocol handling of third-party applications," Miller said in an e-mail exchange. "These same issues got attention again in early July and are similar to the issue referenced in the IE Blog, which is a protocol handler issue, not the issue we released an advisory for [on Oct. 10]. However, after the IE Blog posting on July 18, an issue in URI handling was discussed publicly, and due to increased customer risk due to attack vectors discussed this weekend, and to help reduce confusion between the two issues, Security Advisory 943521 was released yesterday [and] addresses these URI Handler issues, not the previous protocol handler issue."

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"Microsoft has thoroughly investigated the claim of a vulnerability in Internet Explorer and found that this is not a vulnerability in a Microsoft product," the company said in a statement in July.

Full Disclosure security mailing list recipients have been wrangling over whos at fault with that bug. The list of applications affected by the bug includes Skype, Adobe Systems Acrobat Reader, the Netscape browser, Miranda Instant Messenger and the Firefox browser.

The protocol handler flaw involves the launch of arbitrary programs when special URLs containing the % character are clicked on. In doing so, the launched programs may allow spyware to be installed on the users system. The developers of Mozilla have temporarily remedied a similar problem in Firefox in 2.0.6.

Security researcher Juergen Schmidt, with Heise Security, detailed on the Full Disclosure mailing list Oct. 5 how IE 7 passes invalid URIs to Windows XP. In doing so, he also noted that Microsoft had dismissed the vulnerability and said that after a "thorough investigation," Microsoft had determined that it wasnt a vulnerability in a Microsoft product.

After Heise Security notified Skype, the company fixed the problem in 3.5.0.239.

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