Quick FTP Server for Penetration Testing Labs (pyftpdlib)

A minimal FTP file transfer setup for penetration testing labs.
Tested with Kali Linux in local labs and TryHackMe / HTB VPN environments.

This setup is designed for reliable file transfer when upload capability is required during labs or exam-style scenarios.

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🎯 Use case

• Upload files from targets to Kali when upload capability is required
• Works for:
  • Local labs (virt-manager / NAT)
  • TryHackMe / HTB targets via VPN (tun0)
• No system-wide Python installs
• No PEP 668 issues
• No reliance on VM shared folders

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🧠 Design choices

• pyftpdlib is used only when FTP upload capability is required
• Installed inside a dedicated Python virtual environment
• Started via a shell alias (ftpstart)
• Server listens on 0.0.0.0 (all interfaces)
• Alias prints both LAN and VPN IPs for clarity
• Authenticated access only (no anonymous login)

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📦 One-time setup (install once)

1. Create Python virtual environment

python3 -m venv ~/venvs/ftp
source ~/venvs/ftp/bin/activate
pip install pyftpdlib
deactivate

This is done once. You do not reinstall this for every lab.

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2. Add alias to ~/.zshrc

nano ~/.zshrc

Add the following block:

# ===============================
# Quick FTP Server (pyftpdlib)
# ===============================
ftpstart() {
  local PORT="${1:-2121}"
  local USER="${2:-test}"
  local PASS="${3:-Test123!}"
  local VENV="$HOME/venvs/ftp"

  if [[ ! -d "$VENV" ]]; then
    echo "[!] Python venv not found: $VENV"
    return 1
  fi

  source "$VENV/bin/activate" || return 1

  local LANIP TUNIP
  LANIP="$(hostname -I | awk '{print $1}')"
  TUNIP="$(ip -4 -o addr show dev tun0 2>/dev/null | awk '{print $4}' | cut -d/ -f1)"

  echo "[+] FTP server starting"
  echo "    Directory : $(pwd)"
  [[ -n "$LANIP" ]] && echo "    LAN       : ftp://$USER:$PASS@$LANIP:$PORT/"
  [[ -n "$TUNIP" ]] && echo "    VPN       : ftp://$USER:$PASS@$TUNIP:$PORT/"
  echo

  if [[ -n "$LANIP" ]]; then
    echo "    Windows ftp.exe (LAN):"
    echo "      ftp"
    echo "      open $LANIP $PORT"
    echo "      user: $USER"
    echo "      pass: $PASS"
    echo "      binary"
  fi

  if [[ -n "$TUNIP" ]]; then
    echo
    echo "    Windows ftp.exe (VPN):"
    echo "      ftp"
    echo "      open $TUNIP $PORT"
    echo "      user: $USER"
    echo "      pass: $PASS"
    echo "      binary"
  fi

  echo
  echo "    Stop with : CTRL+C"
  echo

  python -m pyftpdlib -p "$PORT" -u "$USER" -P "$PASS" -w
}

Reload your shell:

source ~/.zshrc

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🚀 Usage

Start FTP server (default)

ftpstart

Defaults

• Port: 2121
• User: test
• Password: Test123!
• Directory: current working directory (pwd)

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Custom parameters (port / user / password)

Change directory before starting the server:

cd ~/loot
ftpstart 2121 test S3cr3t!

Format:

ftpstart <PORT> <USER> <PASS>

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🔌 Which IP should be used?

Local Windows VM (virt-manager / NAT)

Use the LAN IP:

192.168.122.x

TryHackMe / HTB target

Use the VPN IP (tun0):

10.x.x.x
192.168.x.x

The server listens on all interfaces (0.0.0.0). The client must connect to an IP it can actually reach.

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🔗 FTP URL notes

The script prints URLs such as:

ftp://test:Test123!@192.168.134.168:2121/

These URLs are intended for:

• GUI clients (FileZilla, WinSCP)
• Tools like curl or wget
• Notes and reporting during labs

⚠️ Important: Windows built-in ftp.exe does not support FTP URL syntax.

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🪟 Windows client notes (ftp.exe)

Use the step-by-step commands printed by the script.

Example:

ftp
open <KALI_IP> 2121
user: test
pass: Test123!
binary

Always use binary when transferring .exe or .dll files. Failure to do so may corrupt binaries during transfer.

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⚠️ FTP passive mode note

If login works but ls, get, or put hangs:

• This is usually caused by FTP passive mode + NAT/VPN

Temporary fix:

python -m pyftpdlib -p 2121 -u test -P Test123! -w --passive-ports 30000-30010

Only required if you encounter this issue.

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🧠 Penetration testing mindset

• Use FTP only when upload capability is required

• Avoid shared folders and GUI copy/paste shortcuts

• Demonstrates understanding of:

  • Interfaces vs routing
  • VPN reachability
  • Reliable file transfer methods
  • Tool limitations (URL vs client syntax)

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✅ Summary

• Install once (virtual environment)
• Start instantly (ftpstart)
• Works for local labs and VPN-based targets
• Clean, repeatable, and lab-safe
• Designed for PNPT-style thinking