Use `sshpass` non-interactively without exposing passwords

Automating Secure Shell (SSH) Access with sshpass: A Guide to Safe, Non-Interactive Use

In the realm of server management and remote operations, SSH (Secure Shell) is an indispensable tool for secure communications. However, while automating SSH commands, the challenge of non-interactively supplying the password poses a barrier. sshpass is a utility designed to handle this scenario, but its use brings up valid concerns regarding the secure handling of passwords. In this blog, we will explore how to use sshpass effectively and safely.

Q1: What is sshpass and why is it useful?

A1: sshpass is a utility for non-interactively performing password authentication with SSH's so-called "password" authentication method. This means you can supply the password for SSH login directly from a script or command line, which facilitates the automation of tasks that involve logging into SSH servers.

Q2: What are some risks associated with using sshpass?

A2: The primary risk involves the exposure of plaintext passwords. If used carelessly, passwords can be visible in process listings (via ps command) or linger in shell history, posing a serious security risk.

Q3: How can I use sshpass securely without exposing passwords in scripts or command lines?

A3: To mitigate security risks while using sshpass: 1. Environment Variables: Store passwords in environment variables temporarily when running scripts. 2. Password Files: Keep passwords in separate files with restricted access, and use sshpass to read from the file. 3. SSH Key Authentication: Where possible, prefer SSH key authentication over passwords for better security.

Background: Practical Applications and Simple Examples

Let's delve into some practical examples to use sshpass in a secure manner respecting the outlined methods above.

Using Environment Variables:

Here, the password is stored in an environment variable and sshpass uses it, without exposing it in the process list or history.

export SSHPASS='your_secure_password'
sshpass -e ssh username@yourserver.com

After executing your script or command, ensure to unset the SSHPASS environment variable for safety.

Using Password Files:

Password files can be safer, provided their permissions are set to be readable only by the owner.

echo 'your_secure_password' > passwordfile
chmod 600 passwordfile
sshpass -f passwordfile ssh username@yourserver.com
rm passwordfile

This method reads the password from a file, uses it, and then you can safely remove the file if it's no longer needed.

Executable Script: Demonstrating sshpass Usage

Below is a simple bash script that demonstrates the use of sshpass with a password file for connecting to a server and executing a command:

#!/bin/bash

# Define server and username
SERVER='yourserver.com'
USERNAME='username'

# Temporary password file
PASSWORD_FILE=$(mktemp)
chmod 600 $PASSWORD_FILE
echo 'your_secure_password' > $PASSWORD_FILE

# Connect to server and run a command
sshpass -f $PASSWORD_FILE ssh $USERNAME@$SERVER 'hostname'

# Clean up
rm $PASSWORD_FILE

This script creates a temporary password file, uses it for SSH login, runs the hostname command on the remote server (to retrieve its hostname), and then cleans up by removing the temporary file.

Conclusion: Securely Using sshpass

Using sshpass in your automation scripts can significantly streamline operations involving frequent SSH logins, yet it demands caution to avoid compromising password security. By employing the techniques shown, such as environment variables and temporary password files, you can maintain a higher level of security. Always aim for SSH keys as a more secure alternative, yet in environments where password use is unavoidable, sshpass, when used wisely, provides a valuable tool.

Further Reading

For further reading related to SSH automation and security, consider exploring the following resources:

• Using SSH Keys for Authentication: Learn about the advantages of SSH key-based authentication over passwords. Digital Ocean: How to Set Up SSH Keys

• Managing SSH Keys: A guide on effectively managing SSH keys to ensure security. Github: Working with SSH key passphrases

• Guide to Secure Shell Configurations: Explore best practices for configuring Secure Shell to enhance security. Cyberciti: 5 Best Practices to Secure and Protect SSH Server

• Advanced SSH Security Tips: Tips and tricks for securing SSH-based communications. TechRepublic: 10 essential SSH security tips for administrators

• Automating SSH Tasks without Passwords: Detailed exploration of automating SSH tasks securely without using passwords. Red Hat Developer: Automating SSH without passwords

These resources provide a comprehensive understanding of the tools and practices to secure and automate SSH access, complementing the use of sshpass with more robust security measures.