Who Killed the Canary: An Exploration into Native Android Security Protections

Despite the more tightly controlled permissions and Java framework used by most programs in the Android operating system, an attacker can use the same classic vulnerabilities that exist for traditional Linux binaries on the programs in the Android operating system. Some classic vulnerabilities include stack overows, string formats, and heap meta-information corruption. Through the exploitation of these vulnerabilities an attacker can hijack the execution ow of an application. After hijacking the execution ow, an attacker can then violate the con_dentiality, integrity, or availability of the operating system. Over the years, the operating systems and compliers have implemented a number of protections to prevent the exploitation of vulnerable programs. The most widely implemented protections include Non-eXecutable stack (NX Stack), Address Space Layout Randomization (ASLR), and Stack Canaries (Canaries). NX Stack protections prevent the injection and execution of arbitrary code through the use of a permissions framework within a program. Whereas, ASLR and Canaries rely on obfuscation techniques to protect control ow, which requires su_cient entropy between each execution. Early in the implementation of these protections in Linux, researchers discovered that without su_cient entropy between executions, ASLR and Canaries were easily bypassed. For example, the obfuscation techniques were useless in programs that ran continuously because the programs did not change the canaries or re-randomize the address space. Similarly, aws in the implementation of ASLR and Canaries in Android only re-randomizes the values after rebooting, which means the address space locations and canary values remain constant across the executions of an Android program. As a result, an attacker can hijack the control ow Android binaries that contain control ow vulnerabilities. The purpose of this paper is to expose these aws and the methodology used to verify their existence in Android versions 4.1 (Jelly Bean) through 8.0 (Oreo).