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Yahoo! leaks! private! key! in! Axis! Chrome! debut!

Extension launch scuppered by certificate blunder

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Yahoo! today released its Axis extension for Chrome – and accidentally leaked its private security key that could allow anyone to create malicious plugins masquerading as official Yahoo! software.

Australian entrepreneur Nik Cubrilovic, who last year garnered notice for identifying Facebook's tracking cookies, revealed the certificate blunder on his blog, and said users should not install the extension “until the issue is clarified”.

Cubrilovic peeked into the extension’s source code and found the private certificate, which Yahoo! uses to sign the application to prove it is genuine and unaltered. The result, he says, is that a miscreant could forge a malicious extension that would be verified by Google's web browser as coming from Yahoo!

There are all sorts of attacks that could be executed with a spoofed extension; the most obvious of these, as Cubrilovic notes, would be to create and sign a traffic logger to capture a victim’s web activity. He wrote:

The certificate file is used by Yahoo! to sign the extension package, which is used by Chrome and the webstore to authenticate that the package comes from Yahoo! With access to the private certificate file a malicious attacker is able to create a forged extension that Chrome will authenticate as being from Yahoo!

The clearest implication is that with the private certificate file and a fake extension you can create a spoofed package that captures all web traffic, including passwords, session cookies, etc. The easiest way to get this installed onto a victim's machine would be to DNS spoof the update URL. The next time the extension attempts to update it will silently install and run the spoofed extension.

He’s also produced a proof-of-concept of a spoofing attack and written up instructions on how to remove the extension.

Yahoo! has since apologised and posted a replacement web search extension that doesn’t include the private half of the security certificate. The new plugin, billed as a search browser, is also available for Firefox, Internet Explorer, Safari, and iPhones and iPads. ®

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