🕷️ Remote Access Backdoor (C)

📌 Overview

This project is a remote access backdoor written in C. It establishes a TCP connection between two programs and allows remote command execution and file transfer.

The goal of this project is to apply networking and low-level C skills and to understand how backdoor-style malware works internally.

🧩 Project Files

• server.c
  Creates a TCP socket, listens on port 8080, accepts one connection, sends commands, uploads files, and receives downloaded files.
• client.c
  Connects to the server, receives commands, executes them, and handles file upload and download.

🌐 Network Implementation

• Protocol: TCP
• Address Family: AF_INET (IPv4)
• Port: 8080
• Blocking sockets
• Single connection only

⚙️ Command Execution

• Commands are sent from the server to the client
• The client executes commands using popen()
• Command output is sent back line by line
• Output ends when the client sends the flag "1"

📁 File Transfer

• download <file>: client reads a local file and sends it to the server
• upload <file>: server sends a file to the client
• File size is sent first as uint64_t
• Endianness handled using htobe64() and be64toh()
• Data sent in chunks of 1024 bytes

📂 Directory Control

• The client supports cd <path>
• Directory change is handled using chdir()

🧱 Implementation Details

• Socket functions: socket(), bind(), listen(), accept(), connect()
• File handling: fopen(), fread(), fwrite()
• File size detection: stat()
• Process execution: popen()

🚀 Build

gcc server.c -o server
gcc client.c -o client

🏁 Runtime Behavior

• Server waits for user input and sends commands
• Client executes received commands
• Communication continues until exit is sent

⚠️ Limitations (As in Code)

• No encryption
• The concept of persistence does not exist
• Does not include techniques to bypass antivirus
• It can be detected by firewals

🎯 Purpose

This project exists to:

• Apply TCP socket programming in C
• Practice low-level file and process handling
• Understand how backdoor-style remote access works
• Analyze insecure remote command execution

🧑‍💻 Author

Lkwads – Cybersecurity Student & Low-Level Programming Enthusiast