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A single web link will WIPE Samsung Android smartphones

Magic number in URL triggers factory reset

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An enterprising hacker has demonstrated how a simple web page can reset various Samsung phones back to the state they left the factory - enabling a click, bump or text to take out a victim's mobe entirely.

The devastating flaw lies in Samsung's dialling software, triggered by the tel protocol in a URL. It isn't applicable to all the company's Android handsets, but those that are vulnerable can have their PIN changed or be wiped completely just by visiting a web page or snapping a bad QR code, or even bonking up against the wrong wireless NFC tag.

The tel protocol is generally used with phone numbers to provide clickable "call me" links on websites: tapping on the hyperlink in the handset's web browser opens up the dialling software and calls the number contained in the link. Such calls aren't made until the fandroid presses a "dial" button, so security is maintained - but some numbers don't require "dial" to be pressed, and it's those which are exploited in this attack.

The best example of an executing number - aka an unstructured supplementary service data message - is *#06#: enter that into just about any GSM phone and it will display the IMEI, the device's serial number. But, importantly, it will do that without one pressing the "dial" button.

That's benign, but try entering *2767*3855# on a Samsung Galaxy S3 and you'll be rewarded with an impossible-to-cancel factory reset before you can say shudda-bought-an-iPhone.

Once one has established that any automatically loaded URL can trigger the behaviour, the attack becomes easy to expand: automatically opening iframes, pushed WAP/USSD messages and NFC tags are capable conduits as elegantly demonstrated over the weekend at Ekoparty 2012:

Not all Samsung handsets are affected; they need to interpret numbers submitted from the browser as though they were typed on the pad, and it seems that some operators have tweaked their handsets to prevent that - although probably not deliberately, it's just a side effect of other changes. Using another web browser should not be effective; there are some claims that Google Chrome is immune, but there are an equal number claiming otherwise.

Samsung hasn't confirmed the attack at the time of writing, but it's safe to assume that a fix will be forthcoming pretty quickly - there's no big technical barrier and Samsung will want to be seen responding rapidly.

The XDA Developers forum has some non-destructive examples should one want to try the hack, but the overall risk should be quite small as the attacker gains nothing from destroying all the data on a phone.

Despite that it might be worth steering clear of unknown URLs, NFC, QR Codes for a while, particularly if they come from smug friends touting new iPhones who might see more humour than most in trashing a Samsung handset or two. ®

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