VPS: Excavating High-Level C++ Constructs from Low-Level Binaries to Protect Dynamic Dispatching

TL;DR

VPS is a binary-level defense mechanism that enhances the security of C++ applications by accurately restricting virtual callsites to valid objects, significantly reducing vtable hijacking risks with moderate performance overhead.

Contribution

VPS introduces a novel binary-level approach that restricts virtual callsites to valid objects, improving accuracy over previous static analysis-based defenses.

Findings

Protects over 97% of virtual callsites in real-world applications

Achieves 9-11% average performance overhead

Identifies 86 false negatives in existing source-based defenses

Abstract

Polymorphism and inheritance make C++ suitable for writing complex software, but significantly increase the attack surface because the implementation relies on virtual function tables (vtables). These vtables contain function pointers that attackers can potentially hijack and in practice, vtable hijacking is one of the most important attack vector for C++ binaries. In this paper, we present VTable Pointer Separation (VPS), a practical binary-level defense against vtable hijacking in C++ applications. Unlike previous binary-level defenses, which rely on unsound static analyses to match classes to virtual callsites, VPS achieves a more accurate protection by restricting virtual callsites to validly created objects. More specifically, VPS ensures that virtual callsites can only use objects created at valid object construction sites, and only if those objects can reach the callsite. Moreover, VPS explicitly prevents false positives (falsely identified virtual callsites) from breaking the binary, an issue existing work does not handle correctly or at all. We evaluate the prototype implementation of VPS on a diverse set of complex, real-world applications (MongoDB, MySQL server, Node.js, SPEC CPU2017/CPU2006), showing that our approach protects on average 97.8% of all virtual callsites in SPEC CPU2006 and 97.4% in SPEC CPU2017 (all C++ benchmarks), with a moderate performance overhead of 11% and 9% geomean, respectively. Furthermore, our evaluation reveals 86 false negatives in VTV, a popular source-based defense which is part of GCC.