The Efficacy of Forward-Edge Control-Flow Integrity in Mitigating Memory Corruption Vulnerabilities : The Case of the Android Stack

Memory corruption is one of the oldest and most prominent problems in the field of computer security. In order to protect the vulnerabilities that arise from memory corruption, a mitigation technique called Control-flow Integrity (CFI) was developed. The Android Open Source Project utilizes a specific implementation of the CFI policy called forward-edge CFI in the compilation of the Android system. However, memory corruption vulnerabilities are still a problem for Android systems. This raises the question: Is forward-edge CFI really effective in mitigating memory corruption vulnerabilities? In this research, the efficacy of forward-edge CFI in terms of mitigating memory corruption vulnerabilities in Android systems is analyzed. This is done by analyzing nine Common Vulnerabilities and Exposures (CVE) in terms of how they can be exploited and whether forward-edge CFI could mitigate them. Additionally, the Android binaries containing the vulnerabilities are analyzed in an attempt to detect the presence of CFI instrumentation. CFI was detected in one of nine vulnerable Android binaries, implying that there exist memory corruption vulnerabilities that forward-edge CFI definitely can not protect. The analysis of nine CVEs showed that five CVEs could be mitigated by forward-edge CFI. These results indicate that forward-edge CFI could definitely mitigate a portion of the memory corruption vulnerabilities plaguing Android systems. However, in order to protect a greater portion of memory corruption vulnerabilities, forward-edge CFI should be combined with other mitigation techniques such as Shadow Stacks