Total Recall: Persistence of Passwords in Android

Abstract

A good security practice for handling sensitive data, such as passwords, is to overwrite the data buffers with zeros once the data is no longer in use. This protects against attackers who gain a snapshot of a device’s physical memory, whether by inperson physical attacks, or by remote attacks like Meltdown and Spectre. This paper looks at unnecessary password retention in Android phones by popular apps, secure password management apps, and even the lockscreen system process. We have performed a comprehensive analysis of the Android framework and a variety of apps, and discovered that passwords can survive in a variety of locations, including UI widgets where users enter their passwords, apps that retain passwords rather than exchange them for tokens, old copies not yet reused by garbage collectors, and buffers in keyboard apps. We have developed solutions that successfully fix these problems with modest code changes.