Advanced Filters, Creating Alpha-Numeric shellcode
Russell Sanfordhad covered in the first article. I felt it necessary to move onto this
next and more advanced topic. In this article I'm going to show you how to
conquer a rather tedious - and ALMOST impossible task: creating shellcode
completely comprised of alphanumeric characters. "Why on earth would we
want to do this?" you may be asking yourself right about now. The answer is
simple. There are several filtering schemes out there being employed by
programs that ONLY allow alphanumeric characters to be passed into their
buffers. Many programmers/hackers will tell you these are impossible to
exploit. In a great deal of ways they are right, but for the most part they are
wrong. Creating alphanumeric shellcode is time-consuming, annoying, and
tiring. Most people simply give up due to the complexity of its creation and
just assume it to be an impossible task. This is why there is little other
documentation like this available to you out there on the net. But, we will go
onto cover this topic in thorough detail. By the end of this article you will
not only be able to create your own code with little effort. But you will know
exactly what obstacles your code will be facing and how to overcome them
when possible. There is one last note I should add before beginning this
article. Due to the complexity of this type of attack and the ratio of
shellcode/original-shellcode, this type of attack will almost never work
against a Windows host. The code covered in this article is intended only for
a Linux box running under an IA32 Intel processor.