How to bypass the Android lock screen with a very long password

Generally when it comes to passwords, longer is considered better.

But try telling that to John Gordon from Texas University who claims to have uncovered a security vulnerability in Android 5.x (Lollipop) which could allow attackers to gain full access to locked devices, even when encryption is enabled. And it’s a particularly long string entered into the password field that could allow a hacker to gain access to your phone’s data and private communications.

Gordon discovered that entering a sufficiently long string into the password field on Android 5.x (before build LMY48M) can crash the device, sending the unauthorised user straight to the Android phone’s home screen.

It’s as though there were never a password in place at all.

Gordon published a YouTube video demonstrating the attack on a Google Nexus 4, and gave further details in a blog post on the University of Texas website.

[ embed video ]

Entering a realllllly long string of characters is made easier if you use the phone’s copy-and-paste feature, as Gordon explains:

Type a few characters, e.g. 10 asterisks. Double-tap the characters to highlight them and tap the copy button. Then tap once in the field and tap paste, doubling the characters in the field. Repeat this process of highlight all, copy, and paste until the field is so long that double-tapping no longer highlights the field. This usually occcurs after 11 or so repetitions.

Potentially that would be one way to fix the problem – limiting the use of copy-and-paste in the device password field.

Alternatively, perhaps it would be sensible if Google’s Android team simply did a sanity check on how many characters had been entered.

Of course, to perform the attack a hacker would need to have physical access to your device. And it goes without saying that you also need to have protected your device with a password, rather than a pattern or PIN code).

Gordon reported the vulnerability to Android’s security team privately back in June, and a fix was released for Nexus users earlier this month.

The flaw has been categorised as being of “moderate” severity, and there is no evidence that it has been exploited in the wild.

However, as we all know, many Android devices are woefully served by security updates – often finding themselves left in the lurch, and remaining vulnerable to bugs that were technically fixed months or years before. Every day that passes for vulnerable Android phones that haven’t received patches increases the chances that someone will take advantage of this and other flaws.

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