Question

1.write three methods to exploit buffer overflow and to archive the goal. If local variables are exploited present all possible approaches.

Goal: The goal is to exploit the program to let it print out “CORRECT SERIAL”. Note: A “Segmentation fault” is fine if the program prints out the desired message.

C programming

Answer 1

Buffers are memory storage regions that temporarily hold data while it is being transferred from one location to another.

A buffer overflow (or buffer overrun) occurs when the volume of data exceeds the storage capacity of the memory buffer. As a result, the program attempting to write the data to the buffer overwrites adjacent memory locations.

For example, a buffer for log-in credentials may be designed to expect username and password inputs of 8 bytes, so if a transaction involves an input of 10 bytes (that is, 2 bytes more than expected), the program may write the excess data past the buffer boundary.

Reason behind the buffer overflow ..

Buffer flow result from malformed inputs or failure to allocate enough space for the buffer. If the transaction overwrites executable code, it can cause the program to behave unpredictably and generate incorrect results, memory access errors, or crashes.

Buffer overflow attack :-Attackers exploit buffer overflow issues by overwriting the memory of an application. This changes the execution path of the program, triggering a response that damages files or exposes private information. For example, an attacker may introduce extra code, sending new instructions to the application to gain access to IT systems.

Types of buffer overflow attacks :-

Stack-based buffer overflows are more common, and leverage stack memory that only exists during the execution time of a function.

Heap-based attacks are harder to carry out and involve flooding the memory space allocated for a program beyond memory used for current runtime operations.

Programming languages that are more vulnerable regarding buffer overflow..-C and C++ are two languages that are highly susceptible to buffer overflow attacks, as they don’t have built-in safeguards against overwriting or accessing data in their memory. Mac OSX, Windows, and Linux all use code written in C and C++.

To prevent buffer overflows :-

Developers can protect against buffer overflow vulnerabilities via security measures in their code, or by using languages that offer built-in protection.

Example of buffer overflow..

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Buffer Overflow Attack with Example
Last Updated: 29-05-2017
A buffer is a temporary area for data storage. When more data (than was originally allocated to be stored) gets placed by a program or system process, the extra data overflows. It causes some of that data to leak out into other buffers, which can corrupt or overwrite whatever data they were holding.

In a buffer-overflow attack, the extra data sometimes holds specific instructions for actions intended by a hacker or malicious user; for example, the data could trigger a response that damages files, changes data or unveils private information.

Attacker would use a buffer-overflow exploit to take advantage of a program that is waiting on a user’s input. There are two types of buffer overflows: stack-based and heap-based. Heap-based, which are difficult to execute and the least common of the two, attack an application by flooding the memory space reserved for a program. Stack-based buffer overflows, which are more common among attackers, exploit applications and programs by using what is known as a stack: memory space used to store user input.

Let us study some real program examples that show the danger of such situations based on the C.

// A C program to demonstrate buffer overflow
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
  
int main(int argc, char *argv[])
{
  
// Reserve 5 byte of buffer plus the terminating NULL.
// should allocate 8 bytes = 2 double words,
// To overflow, need more than 8 bytes...
char buffer[5]; // If more than 8 characters input
// by user, there will be access  
// violation, segmentation fault
  
// a prompt how to execute the program...
if (argc < 2)
{
printf("strcpy() NOT executed....\n");
printf("Syntax: %s <characters>\n", argv[0]);
exit(0);
}
  
// copy the user input to mybuffer, without any
// bound checking a secure version is srtcpy_s()
strcpy(buffer, argv[1]);
printf("buffer content= %s\n", buffer);
  
// you may want to try strcpy_s()
printf("strcpy() executed...\n");
  
return 0;
}

Output of above code will result in :-

Input : 12345678 (8 bytes),
the program run smoothly.
Input : 123456789 (9 bytes)
"Segmentation fault" message will be displayed and the program terminates