What can a buffer overflow do to a program?
Buffer overflow is a vulnerability in low level codes of C and C++. An attacker can cause the program to crash, make data corrupt, steal some private information or run his/her own code. It basically means to access any buffer outside of it’s alloted memory space. This happens quite frequently in the case of arrays.
How many bytes are reserved for echo function?
38 in hex or 56 in decimal bytes are reserved for the local variables of echo function. The address of buffer starts 1c in hex or 28 in decimal bytes before %ebp. This means that 28 bytes are reserved for buffer even though we asked for 20 bytes.
Is there an exploit for buffer overflow in GCC?
The first time I came across the buffer overflow exploit, I couldn’t actually implement it. Many of the existing sources on the web were outdated (worked with earlier versions of gcc, linux, etc). It took me quite a while to actually run a vulnerable program on my machine and exploit it.
How to find the EIP address of a buffer?
We can do it manually by calculating the distance between the buffer start address and the EIP address , We have already got the EIP address so let’s get the start of the buffer. If we type x/24wx $esp it will show us ( x/) 24 ( 24wx) words at the top of the stack ( $esp ).
How to fix buffer overflow in Kapil script?
After func gets over we need to reset the previous stack frame. So set %esp back to %ebp. Then pop the earlier %ebp from stack, store it back in %ebp. So the base pointer register points back to where it pointed in main.
What does it mean to access buffer outside of bound index?
It basically means to access any buffer outside of it’s alloted memory space. This happens quite frequently in the case of arrays. Now as the variables are stored together in stack/heap/etc. accessing any out of bound index can cause read/write of bytes of some other variable.