Researcher reveals easy as pie Android Lollipop lockscreen bypass

Don’t misplace your Nexus phone if you haven’t received Google’s September patch for Android Lollipop and happen to use a password and not a pattern or code to lock the device.

Google’s first monthly patch for Android last Friday for its own Nexus devices included a fix for the bug CVE02015-3860, which it described as a “moderate” severity issue that allowed elevation of privilege from the lockscreen.

But exactly what was capable by exploiting the bug and how difficult it was to exploit wasn’t known until today after a security researcher from the University of Texas published step by step details on how to execute the attack.

In a nutshell, the attack involves overloading the password field with characters when the camera is active, which causes the lock screen to to crash to the unprotected home screen, giving the attacker the ability to run whatever apps they want and full access to data stored on the device.

Two qualifications are that the attacker needs to have possession of the device and that the device is configured with a password lock rather than a pattern or PIN lock.

If those conditions are met, the lockscreen bypass attack begins at the emergency dialer window and involves filling the input field to the brim with characters such as asterisks and after copying the characters, returning to the lockscreen. From there, the attacker would open the camera from the lock screen using the Android swipe and another swipe to expose Android Settings. The last swipe causes a prompt for the user’s password to appear.

The attacker can cause the user interface and the camera app to crash by repeatedly pasting the characters in to the password field, which in turn exposes the unprotected home screen.

From here, the attacker has free rein over the device, which includes using developer access (enabled by Android Debug Bridge) to install malware via a USB connected laptop.

John Gordon, the researcher at University of Texas who reported the bug to Google, told Wired that the scenario he imagined a bug like this could be used in was if a government agent, say at the airport, had access to the device for an extended period.

But, given the attack details are now public, it could be used by any attacker who gained possession of an Nexus device that hasn’t been patched.

Although Gordon only tested the attack on a Nexus device running Android Lollipop, he speculated that other Android devices on the same version could still be vulnerable given that Android patches are unique updates from carriers and OEMs based on fixes that Google makes available.

If non-Nexus Android devices are also vulnerable, it could mean 20 percent of more than one billion Android devices are exposed.

Android OEMS Samsung, LG and HTC all vowed to follow Google in delivering regular monthly security updates following the widespread Stagefright bug revealed in August, though to date none have delivered a September patch.

Interestingly, as noted in Google’s Android issue tracker, the Android Security team initially rated the flaw Gordon found as a low severity bug, which didn’t qualify for payment under Google’s new Android security rewards program.

Gordon however convinced Google in July, a month after reporting the bug, that it warranted a higher severity rating.

“This is a local attack with no user interaction leading to user-level control of the device, essentially "local unprivileged code execution" and I would think it would rank at or just below "remote unprivileged code execution". I hope this rating can be re-evaluated with consideration for the type of attack and extent of device and user data compromise achieved,” wrote Gordon.

Google later upgraded its severity to moderate and offered Gordon a $500 reward.

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