Bug Allows Apps to Bypass Android 4.3 Security Locks

There is a vulnerability in Android 4.3 Jelly Bean that enables a malicious app to disable all of the security locks on a given device, leaving it open to further attacks.

There is a vulnerability in Android 4.3 Jelly Bean that enables a malicious app to disable all of the security locks on a given device, leaving it open to further attacks. Jelly Bean is the most widely deployed version of Android right now.

The vulnerability in Android exists in the way that the operating system handles the flow of events when a user wants to change one of the security locks on a device. There are several different kinds of security locks on Android devices, including PIN codes, facial recognition and gesture locks. When a user wants to change one of these locks, he is asked to enter one of the other ones in order to confirm his control of the device. The vulnerability in Jelly Bean, discovered by researchers at Curesec in Germany, allows a malicious app to skip this step and disable the other security locks.

“The bug exists on the ‘com.android.settings.ChooseLockGeneric class’. This class is used to allow the user to modify the type of lock mechanism the device should have. Android implements several locks, like pin, password, gesture and even face recognition to lock and unlock a device. Before a user can change these settings, the device asks the user for confirmation of the previous lock (e.x. If a user wants to change the pin or remove it it has to first enter the previous pin),” the advisory from Curesec says.

If a malicious app is installed on a vulnerable device, it could control the code flow that determines whether Android enables the mechanism that requires a security code in order to change one of the other security locks. A Google representative said the problem was fixed in Android Kit Kat 4.4.

“We can control the flow to reach the updatePreferencesOrFinish() method and see that IF we provide a Password Type the flow continues to updateUnlockMethodAndFinish(). Above we can see that IF the password is of type PASSWORD_QUALITY_UNSPECIFIED the code that gets executed and effectively unblocks the device. As a result any [rogue] app can at any time remove all existing locks,” the advisory says.

The researchers at Curesec said that they reported the vulnerability to the Android security team at Google on Oct. 11, received a reply the next day and then didn’t get any further feedback from Google after that. The advisory includes a short bit of proof-of-concept code which the researchers say could be used by an installed malicious app. In the comments of their blog post on the bug, the researchers explained that the permissions model in Android can be bypassed with this bug.

“The commandline shown is just a simple PoC so the problem is understood by anyone without needing to write his own application to test it. For executing actions in Android your application needs the exact permission to do this.
For instance an app wants to read SMS or use the Internet, there is a Permission for that. However due the bug you do not need any permission to remove all device locks,” the researchers said.


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