bastion

This is a secure/locked-down bastion implemented as a Docker Container. It uses Alpine Linux as the base image and ships with support for Google Authenticator & DUO MFA support.

It was designed to be used on Kubernetes together with GitHub Authorized Keys to provide secure remote access to production clusters.

MFA Setup & Usage

Here's a demo of what a user experiences when setting up Google Authenticator for the first time.

When using Duo as the MFA provider, this becomes even more magical because Duo supports automatic Push notifications to your mobile device. Just approve the request on your mobile phone (e.g. with a thumb press on iOS) when prompted.

Slack Notifications

Here's what it looks like when someone connects to the bastion if Slack notifications are enabled.

We recommend using Slack notifications for self-reporting.

• Any time a user accesses production systems, they should reply to the slack notification to justify their remote access.
• A "buddy" should approve the login by adding a reaction (e.g. ✅).
• If no one approves the login, it should trigger an incident response to track down the unauthorized access.

---

This project is part of our comprehensive "SweetOps" approach towards DevOps.

It's 100% Open Source and licensed under the APACHE2.

Usage

Running

Refer to the Environment Variables section below to tune how the bastion operates.

$ docker run -p 1234:22 cloudposse/bastion:latest

Building

$ git clone https://github.com/cloudposse/bastion.git
$ cd bastion
$ make docker:build

Testing

Run basic connection tests

$ make test

Configuration

Recommendations

• Do not allow root (or sudo) access to this container as doing so would allow remote users to manipulate audit-logs in /var/log/sudo-io
• Use the bastion as a "jump host" for accessing other internal systems rather than installing a lot of unnecessary stuff, which increases the overall attack surface.
• Sync the contents of /var/log/sudo-io to a remote, offsite location. If using S3, we recommend enabling bucket-versioning.
• Use `github-authorized-keys to automatically provision users; or use the Helm chart.
• Bind-mount /etc/passwd, /etc/shadow and /etc/group into the container as read-only
• Bind-mount /home into container; the bastion does not manage authorized keys

Environment Variables

The following tables lists the most relevant environment variables of the bastion image and their default values.

Duo Settings

Duo is a enterprise MFA provider that is very affordable. Details here: https://duo.com/pricing

ENV	Description	Default
MFA_PROVIDER	Enable the Duo MFA provider	duo
DUO_IKEY	Duo Integration Key
DUO_SKEY	Duo Secret Key
DUO_HOST	Duo Host Endpoint
DUO_FAILMODE	How to fail if Duo cannot be reached	secure
DUO_AUTOPUSH	Automatically send a push notification	yes
DUO_PROMPTS	How many times to prompt for MFA	1

Google Authenticator Settings

Google Authenticator is a free & open source MFA solution. It's less secure than Duo because tokens are stored on the server under each user account.

ENV	Description	Default
MFA_PROVIDER	Enable the Google Authenticator provider	google-authenticator

Enforcer Settings

The enforcer ensures certain conditions are satisfied. Currently, these options are supported.

ENV	Description	Default
ENFORCER_ENABLED	Enable general enforcement	true
ENFORCER_CLEAN_HOME_ENABLED	Erase dot files in home directory before starting session	true

Slack Notifications

The enforcer is able to send notifications to a slack channel anytime there is an SSH login.

ENV	Description	Default
SLACK_ENABLED	Enabled Slack integration	false
SLACK_HOOK	Slack integration method (e.g. pam, sshrc)	sshrc
SLACK_WEBHOOK_URL	Webhook URL
SLACK_USERNAME	Slack handle of bot (defaults to short-dns name)
SLACK_TIMEOUT	Request timeout	2
SLACK_FATAL_ERRORS	Deny logins if slack notification fails	true

SSH Auditor

The SSH auditor uses sudosh to record entire SSH sessions (stdin, stdout, and stderr).

ENV	Description	Default
SSH_AUDIT_ENABLED	Enable the SSH Audit facility	true

This will require that users login with the /usr/bin/sudosh shell.

Update user's default shell by running the command: usermod -s /usr/bin/sudosh $username. By default, root will automatically be updated to use sudosh.

Use the sudoreplay command to audit/replay sessions.

User Accounts & SSH Keys

The bastion does not attempt to manage user accounts. We suggest using GitHub Authorized Keys to provision user accounts and SSH keys. We provide a chart of how we recommend doing it.

Extending

The bastion was written to be easily extensible.

You can extend the enforcement policies by adding shell scripts to etc/enforce.d. Any scripts that are +x (e.g. chmod 755) will be executed at runtime.

Thanks

• @neochrome, for providing a great basic bastion built on top of Alpine Linux
• @aws, for providing detailed instructions on how to do SSH session logging.
• @duo, for providing excellent documentation
• @google for contributing Google Authenticator to the Open Source community

Quick Start

Here's how you can quickly demo the bastion. We assume you have ~/.ssh/authorized_keys properly configured and your SSH key (e.g. ~/.ssh/id_rsa) added to your SSH agent.

$ docker run -it -p 1234:22 \
     -e MFA_PROVIDER=google-authenticator \
     -v ~/.ssh/authorized_keys:/root/.ssh/authorized_keys \
     cloudposse/bastion

Now, in another terminal you should be able to run:

$ ssh root@localhost -p 1234

The first time you connect, you'll be asked to setup your MFA device. Subsequently, each time you connect, you'll be prompted to enter your MFA token.

Help

Got a question? We got answers.

File a GitHub issue, send us an email or join our Slack Community.

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Contributing

Bug Reports & Feature Requests

Please use the issue tracker to report any bugs or file feature requests.

Developing

If you are interested in being a contributor and want to get involved in developing this project or help out with our other projects, we would love to hear from you! Shoot us an email.

In general, PRs are welcome. We follow the typical "fork-and-pull" Git workflow.

1. Fork the repo on GitHub
2. Clone the project to your own machine
3. Commit changes to your own branch
4. Push your work back up to your fork
5. Submit a Pull Request so that we can review your changes

NOTE: Be sure to merge the latest changes from "upstream" before making a pull request!

Copyright

Copyright © 2017-2023 Cloud Posse, LLC

License

See LICENSE for full details.

Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at

  https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied.  See the License for the
specific language governing permissions and limitations
under the License.

Trademarks

All other trademarks referenced herein are the property of their respective owners.

About

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Contributors

Erik Osterman	Marji Cermak