Tracing Stored Program Counter to Detect Polymorphic Shellcode

Abstract

The shellcode use of the polymorphic form has become active as the de facto method for avoiding signature based network security system. We present a new static analysis method for detecting the decryption routine of the polymorphic shellcode. This method traces the processes by which the decryption routine stores the current program counter in a stack, moves the value between registers and uses the value in order to make the address of the encrypted code accessible. Most of decryption routines have the feature which they use the program counter stored on a stack as the address for accessing the memory that the encrypted code is positioned.