Wednesday, August 31, 2011

Mac OS X Can't Properly Revoke Dodgy Digital Certificates

Via PC World -

A programming glitch in Apple's OS X operating system is making it hard for Mac users to tell their computers not to trust digital certificates, exacerbating an ongoing security problem with a Dutch certificate authority that was recently hacked.

Mac users began reporting problems Tuesday when they tried to revoke digital certificates issued by DigiNotar, a Dutch company whose servers were compromised last month and used to issue fraudulent digital certificates. Mac users revoked the certificates on their computers, but still saw some sites that used those certificates being marked as trustworthy.

Digital certificates are an important part of the way the Internet works, and are essential whenever two computers try to connect using the HTTPS protocol. The problem is that Apple's operating system does not allow users to revoke DigiNotar certificates properly, and marks some websites as trustworthy when it shouldn't.


Most users don't revoke digital certificates themselves; they let the browser makers handle it. Chrome, Firefox and Internet Explorer have all blocked DigiNotar certificates, but Apple hasn't said what it plans to do with its Safari browser. That means that, for now, Mac Safari users will have a hard time solving the problem.

Ryan Sleevi, a software developer who has contributed to Google's Chrome project, noticed the issue too. After poking around the Mac OS X source code, though, he uncovered the cause. Users can revoke a certificate using Keychain, but if they happen to visit a site that uses the more-secure Extended Validation Certificates, the Mac will accept the EV certificate even if it's been issued by a certificate authority marked as untrusted in Keychain.

"When Apple thinks you're looking at an EV Cert, they check things differently," Sleevi said in an interview Wednesday. "They override some of your settings and completely disregard them."


It's troubling that such a basic component of Internet security could have such an obvious flaw on the Mac, several security experts said Wednesday. "In a real-world sense, it probably won't affect a lot of people, but for me it's a little bit troubling that the security advice on what you're supposed to do plain doesn't work," said Jeremiah Grossman, chief technology officer with WhiteHat Security.

Apple, which is often tight-lipped about anything to do with computer security, did not return messages Wednesday seeking comment.


Reason #101 not to use Safari, even on Mac OS X.

I personally use Chrome 13 and Firefox 7 Beta on my MBP. Google has already updated Chrome to deal with the DigiNotar incident. Mozilla has released new release versions of Firefox and will be fixing the issue in the beta versions (7) very soon.

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