Command Injection

Introduction

Command Injection occurs when user input is concatenated into system commands executed by the application. In CTF challenges, this often grants full control over the server environment.

Example (Python)

import subprocess

def process_file(filename):
    return subprocess.check_output(['cat', filename])

filename = input('Enter a filename: ')
print(process_file(filename))

Exploit

filename = "file.txt; ls"

Resulting command:

cat file.txt; ls

Tips

Chain commands with ;, &&, or |.
Use blind command injection (e.g., ping -c 1 <collaborator>) to confirm execution.
Try OS-specific payloads if Linux/Windows detection is uncertain.