1. Lunchtime Hackers
Buffer Overflow Intro

2. Some Memory Stuff to Understand
Stack – a segment of memory set aside for a program (kinda like scratch space)
Buffer – just a sement of contiguous memory (not broken up in pieces)
Big Endian – A method of byte ordering (longer history, common in mainframes)
The hex string AB CD EF will be stored in memory as AB CD EF
Little Endian – Different method of byte order interpretation (Your laptop does this)
The hex string AB CD EF will be stored in memory as EF CD AB

3. Linux Permissions Refresher
If you look at Linux perms in the terminal, they’ll look like this:
-rwxrwxrwx <file info> <filename>
We’re interested in the leftmost portion. It can be broken down into a few different parts:
- rwx rwx rwx
First Portion: directory?
Owner Perms
Group Perms
World Perms

4. SUID-bit Allows a program to run as another person
Person usually has higher permissions than person running program
Allows lower permissioned person to do stuff they wouldn’t normally
In a terminal will look like this:
- r - s - -x
Instead of an ‘X’, there is an ‘S’

5. The Code: Set variable called val Set aside buffer of 20 bytes
#include <some libraries>
int main(){
long val=0x ;
char buf[20];
printf("Correct val's value from 0x > 0xdeadbeef!\n");
printf("Here is your chance: ");
scanf("%24s",&buf);
printf("buf: %s\n",buf);
printf("val: 0x%08x\n",val);
if(val==0xdeadbeef)
system("/bin/sh");
else {
printf("WAY OFF!!!!\n");
exit(1); }
return 0;
Set variable called val
Set aside buffer of 20 bytes
Prints to standard out
Reads in 24 bytes (rather than 20 bytes)
If val = 0xDEADBEEF, program drops into a shell