Spill the TeA: An Empirical Study of Trusted Application Rollback Prevention on Android Smartphones

The number and complexity of Trusted Applications (TAs, applications running in Trusted Execution Environments-TEEs) deployed on mobile devices has exploded. A vulnerability in a single TA impacts the security of the entire device. Thus, vendors must rapidly fix such vulnerabilities and revoke vulnerable versions to prevent rollback attacks, i.e., loading an old version of the TA to exploit a known vulnerability. In this paper, we assess the state of TA rollback prevention by conducting a large-scale cross-vendor study. First, we establish the largest TA dataset in existence, encompassing 35,541 TAs obtained from 1,330 firmware images deployed on mobile devices across the top five most common vendors. Second, we identify 37 TA vulnerabilities that we leverage to assess the state of industry-wide TA rollback effectiveness. Third, we make the counterintuitive discovery that the uncoordinated usage of rollback prevention correlates with the leakage of security-critical information and has far-reaching consequences potentially negatively impacting the whole mobile ecosystem. Fourth, we demonstrate the severity of ineffective TA rollback prevention by exploiting two different TEEs on fully-updated mobile devices. In summary, our results indicate severe deficiencies in TA rollback prevention across the mobile ecosystem.