Abstract The lower layers in the modern computing infrastructure are written in languages threatened by exploitation of memory management errors. Recently depl

Abstract The lower layers in the modern computing infrastructure are written in languages threatened by exploitation of memory management errors. Recently deployed exploit mitigations such as control-flow integrity (CFI) can prevent traditional return-oriented programming (ROP) exploits but are much less effective against newer techniques such as Counterfeit Object-Oriented Programming (COOP) that execute a chain of C++ virtual methods. Since these methods are valid control-flow targets, COOP attacks are hard to distinguish from benign computations. Code randomization is likewise ineffective against COOP. Until now, however, COOP attacks have been limited to vulnerable C++ applications which makes it unclear whether COOP is as general and portable a threat as ROP. This paper demonstrates the first COOP-style exploit for Objective-C, the predominant programming language on Apple’s OS X and iOS platforms. We also retrofit the Objective-C runtime with the first practical and efficient defense against our novel attack. Our defense is able to protect complex, real-world software such as iTunes without recompilation. Our performance experiments show that the overhead of our defense is low in practice.