Lftp: Perform Dictionary Attack on SFTP

Welcome to this cybersecurity journey! In this post, we explore how attackers perform a dictionary attack on an SFTP server using the lftp tool to obtain login credentials. If successful, they can upload, edit, or delete files on a compromised server.

What is SFTP?

SFTP (Secure File Transfer Protocol) is an encrypted and secure version of FTP, used for transferring files over a network. It operates over SSH (Secure Shell) to ensure data protection during transit.

What is a Dictionary Attack?

A dictionary attack is a method where an attacker uses a precompiled list of common usernames and passwords (a "dictionary") to guess login credentials repeatedly until access is granted.

What is lftp?

lftp is a Python-based tool that helps in performing dictionary attacks on SFTP servers. Now, let’s see how to clone and use the lftp tool.

Installation

Clone the lftp repository from GitHub:


# Clone lftp repository | To get the code contact us
git clone https://github.com/****/lftp.git
cd lftp
python install.py

After installation, simply type lftp in the terminal to launch the tool.

Usage

When you run lftp, it will prompt you for target details:

Enter Remote Server IP: Provide the target SFTP server's IP address.
Enter Remote Server PORT: Specify the target port (default SFTP port is 22).
Enter Username Wordlist: Provide the path to the username dictionary file.
Enter Password Wordlist: Provide the path to the password dictionary file.
How Many Threads to Use: Specify the number of threads (10-30 recommended for efficiency).

After entering these details, lftp starts the dictionary attack by testing username and password combinations from the dictionary.

Limitations of Dictionary Attacks

1. Time-Consuming

Dictionary attacks rely on testing a large number of passwords, which can take time depending on password complexity.

2. Ineffective Against Login Restrictions

Many servers implement security measures like login rate limits or account lockouts, reducing the effectiveness of dictionary attacks.

3. No Guaranteed Success

If the correct password is not in the dictionary, the attack will fail. Brute-force attacks, which try all possible combinations, offer a more thorough approach.

How to Secure Your Server from Dictionary Attacks

To protect your server from dictionary attacks, implement these best practices:

1. Strong Password Policies

Enforce complex passwords that include uppercase, lowercase, numbers, and special characters to make guessing harder.

2. Account Lockout Rules

Implement account lockout policies after multiple failed login attempts to prevent automated attacks.

3. Use Multi-Factor Authentication (MFA)

Enable MFA to require a second verification step, such as a one-time password (OTP) sent to a mobile device.

4. Regular Password Updates

Encourage users to change their passwords regularly to minimize the risk of stolen credentials being used.

5. Monitoring & Tracking

Use log monitoring tools to detect suspicious login attempts and take action against repeated failed logins.

Disclaimer

This guide is for educational purposes only. The information provided demonstrates how dictionary attacks work and how to secure your server against them.

Warning: Unauthorized access to a system is illegal. Use this knowledge responsibly and only for ethical cybersecurity research.