Apple issues fix for "embarrassing" Mac flaw

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Security certificate flaw quickly patched by Apple, and experts advise updating Macs immediately

Apple has issued fixes for a security flaw in its Mac computers that allows hackers to intercept data such as email, patching a major and embarrassing glitch that came to light several days ago.

The security update for users of Apple's OS X computer operating software follows a fix issued for iPhones last week, meaning all Apple device users now have access to the patch.

The flaw allowed attackers with access to a mobile user's network, such as a shared unsecured wireless service offered by a cafe, to see or alter exchanges between the user and protected sites such as Google's Gmail or Facebook.

Governments with access to telecom carrier data could do the same, experts said.

The flaw was related to the way in which well-understood protocols were implemented, and how Apple's software recognises digital certificates used by websites to establish encrypted connections.

Security expert Graham Cluley called the flaw "embarrassing", saying it was caused by a programmer including a "goto fail" line twice in succession, where it was only needed once. "The first one is in the right place, but the second shouldn’t be there," he noted. "That duplicate line wrecks the code’s intended execution path, meaning that a critical authentication check doesn’t occur."

Researchers have said the bug could have been present for months. Apple has not said when or how it learned about the flaw in the way iOS handles sessions, in what are known as secure sockets layer (SSL) or transport layer security. Nor has it said whether the flaw was being exploited.

Apple said in a statement that the Mac security update also improved features such as its FaceTime videoconferencing service and email.

Update now

Experts advised users to update their systems immediately.

"It is now obviously important that iMac and MacBook users update their copy of Mavericks at the earliest opportunity (users of earlier versions of Mac OS X are not thought to be affected), before online criminals manage to take advantage of the flaw," said Cluley.

"I would certainly encourage users to upgrade to OS X Mavericks 10.9.2, but it’s always sensible to make a secure backup of your computer first, just in case," he added.

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