1. Smashing the Stack for Fun and Profit
-by aleph1 circa 1996
Presented by Dan Frohlich

2. Overview Memory and Stack basics. The buffer overflow vulnerability.
Take control.
Spawn a shell.
Issues.
Guesswork and Increasing your chance of success.
Questions?

3. Memory Basics.
The Code or Text section is usually read only, preventing self-modifying code.

4. A Stack Frame. Pushed to stack on function CALL
The return address is copied to the CPU Instruction Pointer when the function returns and it’s stack frame is POP’d.

5. The buffer overflow vulnerability.
The user injected data writes beyond the unchecked buffer length, overwriting the stack frame return address!

6. Take control. The last byte of the buffer is the return address.
To run arbitrary code of the users choice, set to the address of the buffer.

7. Spawn a shell. Write code such that a shell if spawned.
provides platform independent code to spawn a shell.
Shell command is executed in the program’s security context .
Allows user impersonation
If program is running as root, the user now has total control of the host!

8. Issues. What to exploit? What is the return address?
grep is your friend
grep the source for strcpy, strcat, etc.
What is the return address?
Can not be known at runtime. Must be guessed.
Dealing with small buffers.
Place shell code in an environment variable.

9. Guesswork and Increasing your chance of success.
Stack sizes are application dependant but 100 to 1000 bytes are good guesses.
Prolog your exploit with NOOPs!

10. Questions? aleph1 uses a combination of JMP and CALL in his buffer.
Why is this necessary?
Can’t you just right buffer of NOOPs followed by the return address of the shell command environment variable?