Write an exploit / attack for the scanf function. Explain how the given buffer overflow attack works. Hint: write second program that spits out input.

Deliverables: - discussion of the buffer overflow attack.

                        - stack diagram of the given code execution.

                                    -- valid input.

                                    --invalid input (input that causes function bar to be called.

                        - exploit of scanf.

                        - brief discussion on how to prevent buffer overflows.

#include

#include

void foo (const char * input)

{

            char buf [50];

            printf ("My stack looks like: \n%p\n%p\n%p\n%p\n%p\n%p\n%p\n\n");

strcpy (buf,"I am Bender. Please Insert Girder");

strcat (buf,input);

printf ("%s\n",buf);

printf ("My stack looks like: \n%p\n%p\n%p\n%p\n%p\n%p\n%p\n\n");

return;

}

void bar ()

{

            printf ("Auug! I've been hacked!\n");

            return;

}

int main (int argc, char*argv[])

{

            scanf("%s",buf);

            printf ("address of foo: %p\n",foo);

            printf ("address of bar: %p\n", bar);

            foo (buf);

            return 0;

}

Example Stack Diagram:

Stack diagram for the strcat function at the beginning of function foo.