webssh2/README.md

WebSSH2 - Web SSH Client

WebSSH2 is an HTML5 web-based terminal emulator and SSH client. It uses SSH2 as a client on a host to proxy a Websocket / Socket.io connection to an SSH2 server.

Table of Contents

• Requirements
• Breaking Changes
• Installation
• Docker Setup
• Usage
• Configuration
• Features
• Routes
• Client-Side Module
• Tips
• Support

Requirements

• Node.js 6.9.1

Breaking Changes

• See CONFIG.md for a list of breaking changes to the config.json file.
• See DEPRECATED.md for a list of deprecated options.

Installation

1. Clone the repository:

   git clone https://github.com/billchurch/webssh2.git
   cd webssh2
   

2. Install dependencies:

   npm install --production
   

   For development purposes, use npm install instead.

3. Configure the application by editing config.json if needed.

4. Start the server:

   npm start
   

Docker Setup

1. Build and run the Docker container (with debug messages):

   docker build -t webssh2 .
   docker run --name webssh2 --rm -it -p 2222:2222 -e "DEBUG=webssh2*,-webssh2:ssh2" webssh2
   

Important Note About Configuration Files

As of recent versions, the configuration file location has moved from /usr/src to /usr/src/app in the Docker container. This change improves organization but requires attention when mounting custom configuration files.

To use a custom configuration file with the Docker container, mount your config.json to the new location using:

docker run -it --rm --name webssh2 \
  -p 2222:2222 \
  -e DEBUG="webssh2*" \
  -v "$(pwd)/config.json:/usr/src/app/config.json" \
  billchurch/webssh2:bigip-server

Note:

• If you previously mounted your configuration file to /usr/src/config.json, it will not be detected. The container will silently fall back to default configuration.
• The new location at /usr/src/app/config.json is the only valid path for custom configuration files.
• The default configuration provides basic functionality, so missing custom configurations may not be immediately apparent.

Usage

Access the web client by navigating to:

http://localhost:2222/ssh

You'll be prompted for host details and SSH credentials.

Alternatively you may use the /ssh/host/<host> route:

http://localhost:2222/ssh/host/127.0.0.1

You'll be prompted for SSH credentials via HTTP Basic Authentication. P

Configuration

GET Parameters

• port= - integer - SSH server port (default: 22)
• header= - string - Optional header text
• headerBackground= - string - Optional background color (default: "green")
• sshterm= - string - Terminal type for pty (default: xterm-color)

Config File Options

Edit config.json to customize the following options:

• listen.ip - string - IP address to listen on (default: "127.0.0.1")
• listen.port - integer - Port to listen on (default: 2222)
• http.origins - array - CORS origins for socket.io (default: ["*:*"])
• user.name - string - Default SSH username (default: null)
• user.password - string - Default SSH password (default: null)
• ssh.host - string - Default SSH host (default: null)
• user.privatekey - string - Default SSH private key (default: null)
• ssh.port - integer - Default SSH port (default: 22)
• ssh.term - string - Terminal emulation (default: "xterm-color")
• ssh.readyTimeout - integer - SSH handshake timeout in ms (default: 20000)
• ssh.keepaliveInterval - integer - SSH keepalive interval in ms (default: 120000)
• ssh.keepaliveCountMax - integer - Max SSH keepalive packets (default: 10)
• ssh.disableInteractiveAuth - boolean - When set to true, prevents interactive authentication through the web interface. Users must use Basic Authentication via the /ssh/host/<host> route. (default: false)
• ssh.algorithms.cipher - array - Supported cipher algorithms (default: ["aes128-ctr", "aes192-ctr", "aes256-ctr", "aes128-gcm", "aes128-gcm@openssh.com", "aes256-gcm", "aes256-gcm@openssh.com", "aes256-cbc"])
• ssh.algorithms.compress - array - Supported compression methods (default: ["none", "zlib@openssh.com", "zlib"])
• ssh.algorithms.hmac - array - Supported HMAC algorithms (default: ["hmac-sha2-256", "hmac-sha2-512", "hmac-sha1"])
• ssh.algorithms.kex - array - Supported key exchange methods (default: ["ecdh-sha2-nistp256", "ecdh-sha2-nistp384", "ecdh-sha2-nistp521", "diffie-hellman-group-exchange-sha256", "diffie-hellman-group14-sha1"])
• ssh.algorithms.serverHostKey - array - Supported host key types (default: ["ecdsa-sha2-nistp256", "ecdsa-sha2-nistp384", "ecdsa-sha2-nistp521", "ssh-rsa"])
• header.text - string - Header text (default: null)
• header.background - string - Header background color (default: "green")
• session.name - string - Session cookie name (default: "webssh2.sid")
• session.secret - string - Session secret key (default: crypto.randomBytes(32).toString("hex"))
• options.challengeButton - boolean - Enable challenge button (default: true)
• options.autoLog - boolean - Enable auto-logging (default: false)
• options.allowReauth - boolean - Allow reauthentication (default: true)
• options.allowReconnect - boolean - Allow reconnection (default: true)
• options.allowReplay - boolean - Allow credential replay (default: true)

For detailed SSH algorithm configurations, refer to the full config file.

Features

Keyboard Interactive Authentication

Keyboard Interactive authentication provides a flexible way to handle various authentication scenarios, including multi-factor authentication.

How it works

1. When the SSH server requests Keyboard Interactive authentication, WebSSH2 can handle it in two ways: a) Automatically (default behavior) b) By prompting the user through the web interface

2. In automatic mode:

   • If all prompts contain the word "password" (case-insensitive), WebSSH2 will automatically respond using the password provided during the initial connection attempt.
   • If any prompt doesn't contain "password", all prompts will be forwarded to the web client for user input.

3. When prompts are sent to the web client:

   • A dialog box appears in the user's browser, displaying all prompts from the SSH server.
   • The user can input responses for each prompt.
   • Responses are sent back to the SSH server to complete the authentication process.

Configuration Options

You can customize the Keyboard Interactive authentication behavior using the following option in your config.json:

{
  "ssh": {
    "alwaysSendKeyboardInteractivePrompts": false
  }
}

• alwaysSendKeyboardInteractivePrompts (boolean, default: false):
  • When set to true, all Keyboard Interactive prompts will always be sent to the web client, regardless of their content.
  • When set to false (default), WebSSH2 will attempt to automatically handle password prompts and only send non-password prompts to the web client.

Use Cases

1. Simple Password Authentication: With default settings, if the SSH server uses Keyboard Interactive for password authentication, WebSSH2 will automatically handle it without additional user interaction.

2. Multi-Factor Authentication: For SSH servers requiring additional factors (e.g., OTP), WebSSH2 will present prompts to the user through the web interface.

3. Always Prompt User: By setting alwaysSendKeyboardInteractivePrompts to true, you can ensure that users always see and respond to all authentication prompts, which can be useful for security-sensitive environments or for debugging purposes.

Security Considerations

• The automatic password handling feature is designed for convenience but may not be suitable for high-security environments. Consider setting alwaysSendKeyboardInteractivePrompts to true if you want users to explicitly enter their credentials for each session.
• Ensure that your WebSSH2 installation uses HTTPS to protect the communication between the web browser and the WebSSH2 server.

For more information on SSH keyboard-interactive authentication, refer to RFC 4256.

SSH Private Key Authentication

WebSSH2 supports SSH private key authentication when using the /ssh/host/ endpoint with a private key configured in the server settings.

Configuration

Private key authentication can only be configured through the config.json file:

{
  "user": {
    "name": "myuser",
    "privatekey": "-----BEGIN RSA PRIVATE KEY-----\nYour-Private-Key-Here\n-----END RSA PRIVATE KEY-----",
    "password": "optional-fallback-password"
  }
}

Key Requirements

• Only ssh-rsa type keys are supported
• The private key must be in PEM format
• The key in config.json must be on a single line with \n as line separators
• Must include the appropriate header and footer:

  -----BEGIN RSA PRIVATE KEY-----\n[... key content ...]\n-----END RSA PRIVATE KEY-----
  

Generating a Private Key

To generate a new SSH private key, you can use the following command:

ssh-keygen -m PEM -t rsa -b 4096 -f ~/.ssh/id_rsa

Converting Your Private Key

To convert your existing SSH private key into the correct format for config.json, you can use this bash command:

echo '"'$(cat ~/.ssh/id_rsa | tr '\n' '~' | sed 's/~/\\n/g')'"'

This command:

1. Reads your private key file
2. Converts newlines to temporary characters
3. Replaces those characters with \n
4. Wraps the result in quotes
5. Outputs the key in a format ready to paste into your config.json

Authentication Process

1. When connecting through the /ssh/host/ endpoint, WebSSH2 will first attempt to authenticate using the private key specified in config.json
2. If key authentication fails and user.password is configured, the system will automatically attempt password authentication
3. If both authentication methods fail, you'll receive an authentication error

Endpoint Support

• /ssh/host/:host - Supports private key authentication configured via config.json
• /ssh - Does NOT support private key authentication

Security Considerations

• Store private keys securely in your server configuration
• Use appropriate file permissions for your config.json file
• Consider using encrypted private keys for additional security
• Always use HTTPS when accessing the WebSSH2 service

Example Usage

1. Convert and configure your private key:

   # First, convert your key
   echo '"'$(cat ~/.ssh/id_rsa | tr '\n' '~' | sed 's/~/\\n/g')'"'
   
   # Copy the output and paste it into config.json
   

2. Configure config.json:

   {
     "user": {
       "name": "myuser",
       "privatekey": "-----BEGIN RSA PRIVATE KEY-----\nMIIEpA...[rest of key]...Yh5Q==\n-----END RSA PRIVATE KEY-----",
       "password": "fallback-password"
     }
   }
   

3. Access the service via the /ssh/host/ endpoint:

   https://your-server:2222/ssh/host/target-server
   

Troubleshooting

If key authentication fails, check:

• Key type is ssh-rsa
• Key format in config.json is properly escaped with \n line separators
• Key permissions on the target SSH server
• Server's authorized_keys file configuration
• SSH server logs for specific authentication failure reasons

For additional support or troubleshooting, please open an issue on the GitHub repository.

Environment Variables via URL

WebSSH2 supports passing environment variables through URL parameters, allowing you to customize the SSH session environment. This feature enables scenarios like automatically opening specific files or setting custom environment variables.

Server Configuration

Before using this feature, you must configure your SSH server to accept the environment variables you want to pass. Edit your /etc/ssh/sshd_config file to include the desired variables in the AcceptEnv directive:

# Allow client to pass locale environment variables and custom vars
AcceptEnv LANG LC_* VIM_FILE CUSTOM_ENV

Remember to restart your SSH server after making changes:

sudo systemctl restart sshd  # For systemd-based systems
# or
sudo service sshd restart   # For init.d-based systems

Usage

Pass environment variables using the env query parameter:

# Single environment variable
http://localhost:2222/ssh/host/example.com?env=VIM_FILE:config.txt

# Multiple environment variables
http://localhost:2222/ssh/host/example.com?env=VIM_FILE:config.txt,CUSTOM_ENV:test

Security Considerations

To maintain security, environment variables must meet these criteria:

• Variable names must:
  • Start with a capital letter
  • Contain only uppercase letters, numbers, and underscores
  • Be listed in the SSH server's AcceptEnv directive
• Variable values cannot contain shell special characters (;, &, |, `, $)

Invalid environment variables will be silently ignored.

Example Usage

1. Configure your SSH server as shown above.

2. Create a URL with environment variables:

   http://localhost:2222/ssh/host/example.com?env=VIM_FILE:settings.conf,CUSTOM_ENV:production
   

3. In your remote server's .bashrc or shell initialization file:

   if [ ! -z "$VIM_FILE" ]; then
     vim "$VIM_FILE"
   fi
   
   if [ ! -z "$CUSTOM_ENV" ]; then
     echo "Running in $CUSTOM_ENV environment"
   fi
   

Troubleshooting

If environment variables aren't being set:

1. Verify the variables are permitted in /etc/ssh/sshd_config
2. Check SSH server logs for any related errors
3. Ensure variable names and values meet the security requirements
4. Test with a simple variable first to isolate any issues

Routes

WebSSH2 provides two main routes:

1. /ssh

• URL: http(s)://your-webssh2-server/ssh
• Features:

  • Interactive login form

    

  • Terminal configuration options

    

2. /ssh/host/:host

• URL: http(s)://your-webssh2-server/ssh/host/:host
• Authentication: HTTP Basic Auth
• Features:
  • Quick connections to specific hosts
  • Optional port parameter (e.g., ?port=2222)

Client-Side Module

WebSSH2 uses a companion module called webssh2_client which provides the browser-side terminal interface and WebSocket communication layer.

About webssh2_client

• Repository: https://github.com/billchurch/webssh2_client
• Purpose: Provides the browser-based terminal emulator and WebSocket client
• Integration: Automatically included as a dependency in package.json
• Version: The compatible version is managed through the package.json dependency

Features

The client module provides:

• Terminal emulation using xterm.js
• WebSocket communication with the WebSSH2 server
• User interface for SSH connections
• Terminal configuration and customization
• Session management
• File transfer capabilities

Client-Server Communication

The server integrates with the client module by:

1. Serving the client's static files from /client/public
2. Injecting server configuration into the client via window.webssh2Config
3. Managing WebSocket connections for terminal I/O
4. Handling authentication and session management

Customization

More to follow...

Tips

• For security, use HTTPS when transmitting credentials via HTTP Basic Auth.
• Terminal settings for /ssh/host/:host can be customized after login via Menu | Settings and persist across sessions.
• You can enable debug from the console by passing the DEBUG environment variable to your start script: DEBUG=webssh*,-webssh2:ssh2 npm run start. The webssh2:ssh2 namespace is very chatty and shows all of the SSH protocol information, the -webssh2:ssh2 excludes that namespace from the line above, otherwise DEBUG=webssh* will capture all of the WebSSH2 specific bits. You may also debug Socket.IO and Express related events with engine, socket and express namespaces, or go for broke and debug everything with DEBUG=*.
• For development information see DEVELOPMENT.md.

For more detailed information on configuration and usage, please refer to the full documentation or open an issue on GitHub.

Support

If you like what I do, and want to support me you can buy me a coffee!