The smart card is now considered a secure system. However, it is possible, using certain types of attacks, obtain information. In this article, we present how this information has revealed the implementation used by a smart card to call native code from Java Card world. Once apprehended this mechanism, we used to run our own native code. This code, when run with the privileges of the operating system, we were able to read ROM and get all the codes of the contested map. An evaluation of this attack on cards of different models is presented in conclusion.