S.T.R.E.S.S. : Stress Testing and Reverse Engineering for System Security

In modern wireless networks the functions included into layer II have to deal with complex problems, such as security and access control, that were previously demanded to upper layers. This growing complexity led some vendors to implement layer II primitives directly in software, e.g. IEEE 802.11i has been largely distributed as a software patch to be used with legacy 802.11b/g hardware. In any extremely complex software the likelihood of committing errors during the implementation raises, and it is well known that software bugs can lead to instability of the system and possibly to security vulnerability. Software bugs are the most common cause of successful attacks against any kind of network and represent a real plague for system administrators. Stress test is a widely used methodology to find and eliminate software bugs. In this paper we present a platform to perform a stress test of generic network protocols implementations but especially optimized for Layer II stress tests, that present specific problems. With our approach a generic network protocol described with ABNF language can be tested transmitting arbitrary frame sequences and interpreting the responses to verify consistence with the communication standard used. Our platform can interact dynamically with the tested machine (an access point, a router etc.) to verify its robustness and its compliance with the standard. Experiments confirmed the validity of our approach both as a stress test technique for system under development and as a reverse engineering technique for interaction with closed source system.