My First Writeup: Buffer Overflow Basics

by

This is my first CTF writeup, covering the basics of a buffer overflow vulnerability.

Introduction

Buffer overflow is a common vulnerability that occurs when a program attempts to write data to a buffer beyond its allocated size. This can overwrite adjacent memory locations, leading to various issues, including program crashes, unexpected behavior, or even arbitrary code execution.

The Challenge

[Describe the CTF challenge here, e.g., a simple C program with a vulnerable strcpy function.]

#include <stdio.h>
#include <string.h>

void vulnerable_function(char *input) {
    char buffer[16];
    strcpy(buffer, input);
    printf("Input: %s\n", buffer);
}

int main(int argc, char **argv) {
    if (argc < 2) {
        printf("Usage: %s <input>\n", argv[0]);
        return 1;
    }
    vulnerable_function(argv[1]);
    return 0;
}

Exploitation

[Explain the exploitation steps, e.g., finding the offset, crafting the payload with shellcode and return address.]

We can use tools like GDB or Pwntools to analyze the stack and determine the offset to overwrite the return address. Once the offset is found, we can craft a payload consisting of NOP sleds, shellcode, and the overwritten return address pointing to our shellcode.

Conclusion

This writeup demonstrated a basic buffer overflow exploitation. Understanding these fundamental vulnerabilities is crucial for both offensive and defensive cybersecurity.

```