VScape: Assessing and Escaping Virtual Call Protections

Many control-flow integrity (CFI) solutions have been proposed to protect indirect control transfers (ICT), including C++ virtual calls. Assessing the security guarantees of these defenses is thus important but hard. In practice, for a (strong) defense, it usually requires abundant manual efforts to assess whether it could be bypassed, when given a specific (weak) vulnerability. Existing automated exploit generation solutions, which are proposed to assess the exploitability of vulnerabilities, have not addressed this issue yet.

In this paper, we point out that a wide range of virtual call protections, which do not break the C++ ABI (application binary interface), are vulnerable to an advanced attack COOPLUS, even if the given vulnerabilities are weak. Then, we present a solution VScape to assess the effectiveness of virtual call protections against this attack. We developed a prototype of VScape, and utilized it to assess 11 CFI solutions and 14 C++ applications (including Firefox and PyQt) with known vulnerabilities. Results showed that real-world applications have a large set of exploitable virtual calls, and VScape could be utilized to generate working exploits to bypass deployed defenses via weak vulnerabilities.