win()function (or equivalent); once you successfully redirect execution there, you complete the challenge.
Segmentation Faultmessage, in combination with radare2, to tell when we overwrote EIP. There is a better way to do it than simple brute force (we'll cover this in the next post), but it'll do for now.
flag()function in the binary. This is simple.
flag()function is at
As that we sent became
0x41- which is the ASCII code of
A. So the solution is simple - let's just find the characters with ascii codes
pause()to give us time to attach
radare2onto the process.
python3 exploit.pyand then open up a new terminal window.
unsafe()and read the value of the return pointer.
0xc3910408- look familiar? It's the address we were trying to send over, except the bytes have been reversed, and the reason for this reversal is endianness. Big-endian systems store the most significant byte (the byte with the largest value) at the smallest memory address, and this is how we sent them. Little-endian does the opposite (for a reason), and most binaries you will come across are little-endian. As far as we're concerned, the byte are stored in reverse order in little-endian executables.
radare2comes with a nice tool called
rabin2for binary analysis:
p32()function ready for use!
bytesrather than a string, so you have to make the padding a byte string: