Buffer Overflow Attack: Understanding, Implementation, and Exploitation

Buffer overflow is a type of software vulnerability that allows an attacker to overwrite memory locations beyond the boundary of a buffer, potentially leading to a crash or arbitrary code execution. This occurs when a program attempts to store more data in a buffer than its allocated capacity, causing the extra data to overwrite adjacent memory locations.

Here's an example of a vulnerable program that reads a string from the user and stores it in a fixed-size buffer:

#include <stdio.h>

int main()
{
    char buffer[4];
    printf("Enter your name: ");
    gets(buffer);
    printf("Hello, %s!
", buffer);
    return 0;
}

In this program, the gets() function reads user input and stores it in the buffer variable, which has a size of 4 bytes. However, if the user enters a string longer than 4 bytes, it will overwrite adjacent memory locations, resulting in undefined behavior.

To exploit this vulnerability, an attacker can provide input exceeding 4 bytes, including malicious code. This code can then be executed by overwriting the return address on the stack with the address of the attacker's code.

Here's an example of an exploit that launches a shell:

#include <stdio.h>

void shell()
{
    printf('Launching shell...
');
    system("/bin/sh");
}

int main()
{
    char buffer[4];
    printf("Enter your name: ");
    gets(buffer);
    printf("Hello, %s!
", buffer);
    return 0;
}

In this exploit, the shell() function is defined to launch a shell, and the return address on the stack is overwritten with the address of this function. When the vulnerable program returns from the main() function, it will jump to the shell() function instead of returning to the caller.

Here's a screenshot of the vulnerable program being exploited:

As you can see, the exploit launches a shell, granting the attacker access to the system. This is just one example of how buffer overflow vulnerabilities can be exploited, highlighting the importance of secure coding practices and using safe functions to prevent these attacks.