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Proxy over your Docker socket to restrict which requests it accepts
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README.md #7 - privileged explanation 2018-05-21 10:45:42 +01:00

README.md

Docker Socket Proxy

What?

This is a security-enhaced proxy for the Docker Socket.

Why?

Giving access to your Docker socket could mean giving root access to your host, or even to your whole swarm, but some services require hooking into that socket to react to events, etc. Using this proxy lets you block anything you consider those services should not do.

How?

We use the official Alpine-based HAProxy image with a small configuration file.

It blocks access to the Docker socket API according to the environment variables you set. It returns a HTTP 403 Forbidden status for those dangerous requests that should never happen.

Security recommendations

  • Never expose this container's port to a public network. Only to a Docker networks where only reside the proxy itself and the service that uses it.
  • Revoke access to any API section that you consider your service should not need.
  • This image does not include TLS support, just plain HTTP proxy to the host Docker Unix socket (which is not TLS protected even if you configured your host for TLS protection). This is by design because you are supposed to restrict access to it through Docker's built-in firewall.
  • Read the docs for the API version you are using, and know what you are doing.

Usage

  1. Run the API proxy (--privileged flag is required here because it connects with the docker socket, which is a privileged connection in some SELinux/AppArmor contexts and would get locked otherwise):

    $ docker container run \
    -d --privileged \
    --name dockerproxy \
    -v /var/run/docker.sock:/var/run/docker.sock \
    -p 127.0.0.1:2375:2375 \
    tecnativa/docker-socket-proxy

  2. Connect your local docker client to that socket:

    $ export DOCKER_HOST=tcp://localhost

  3. You can see the docker version:

    $ docker version
Client:
 Version:      17.03.1-ce
 API version:  1.27
 Go version:   go1.7.5
 Git commit:   c6d412e
 Built:        Mon Mar 27 17:14:43 2017
 OS/Arch:      linux/amd64

Server:
 Version:      17.03.1-ce
 API version:  1.27 (minimum version 1.12)
 Go version:   go1.7.5
 Git commit:   c6d412e
 Built:        Mon Mar 27 17:14:43 2017
 OS/Arch:      linux/amd64
 Experimental: false

  4. You cannot see running containers:

    $ docker container ls
Error response from daemon: <html><body><h1>403 Forbidden</h1>
Request forbidden by administrative rules.
</body></html>

The same will happen to any containers that use this proxy's 2375 port to access the Docker socket API.

Grant or revoke access to certain API sections

You grant and revoke access to certain features of the Docker API through environment variables.

Normally the variables match the URL prefix (i.e. AUTH blocks access to /auth/* parts of the API, etc.).

Possible values for these variables:

  • 0 to revoke access.
  • 1 to grant access.

Access granted by default

These API sections are mostly harmless and almost required for any service that uses the API, so they are granted by default.

  • EVENTS
  • PING
  • VERSION

Access revoked by default

Security-critical

These API sections are considered security-critical, and thus access is revoked by default. Maximum caution when enabling these.

  • AUTH
  • SECRETS
  • POST: When disabled, only GET and HEAD operations are allowed, meaning any section of the API is read-only.

Not always needed

You will possibly need to grant access to some of these API sections, which are not so extremely critical but can expose some information that your service does not need.

  • BUILD
  • COMMIT
  • CONTAINERS
  • EXEC
  • IMAGES
  • INFO
  • NETWORKS
  • NODES
  • PLUGINS
  • SERVICES
  • SWARM
  • SYSTEM
  • TASKS
  • VOLUMES

Supported API versions

Feedback

Please send any feedback (issues, questions) to the issue tracker.