jupyterhub/docs/source/explanation/websecurity.md

(web-security)=

# Security Overview

The **Security Overview** section helps you learn about:

- the design of JupyterHub with respect to web security
- the semi-trusted user
- the available mitigations to protect untrusted users from each other
- the value of periodic security audits

This overview also helps you obtain a deeper understanding of how JupyterHub
works.

## Semi-trusted and untrusted users

JupyterHub is designed to be a _simple multi-user server for modestly sized
groups_ of **semi-trusted** users. While the design reflects serving
semi-trusted users, JupyterHub can also be suitable for serving **untrusted** users.

As a result, using JupyterHub with **untrusted** users means more work by the
administrator, since much care is required to secure a Hub, with extra caution on
protecting users from each other.

One aspect of JupyterHub's _design simplicity_ for **semi-trusted** users is that
the Hub and single-user servers are placed in a _single domain_, behind a
[_proxy_][configurable-http-proxy]. If the Hub is serving untrusted
users, many of the web's cross-site protections are not applied between
single-user servers and the Hub, or between single-user servers and each
other, since browsers see the whole thing (proxy, Hub, and single user
servers) as a single website (i.e. single domain).

## Protect users from each other

To protect users from each other, a user must **never** be able to write arbitrary
HTML and serve it to another user on the Hub's domain. This is prevented by JupyterHub's
authentication setup because only the owner of a given single-user notebook server is
allowed to view user-authored pages served by the given single-user notebook
server.

To protect all users from each other, JupyterHub administrators must
ensure that:

- A user **does not have permission** to modify their single-user notebook server,
  including:
  - the installation of new packages in the Python environment that runs
    their single-user server;
  - the creation of new files in any `PATH` directory that precedes the
    directory containing `jupyterhub-singleuser` (if the `PATH` is used
    to resolve the single-user executable instead of using an absolute path);
  - the modification of environment variables (e.g. PATH, PYTHONPATH) for
    their single-user server;
  - the modification of the configuration of the notebook server
    (the `~/.jupyter` or `JUPYTER_CONFIG_DIR` directory).
  - unrestricted selection of the base environment (e.g. the image used in container-based Spawners)

If any additional services are run on the same domain as the Hub, the services
**must never** display user-authored HTML that is neither _sanitized_ nor _sandboxed_
(e.g. IFramed) to any user that lacks authentication as the author of a file.

## Mitigate security issues

The several approaches to mitigating security issues with configuration
options provided by JupyterHub include:

### Enable subdomains

JupyterHub provides the ability to run single-user servers on their own
subdomains. This means the cross-origin protections between servers has the
desired effect, and user servers and the Hub are protected from each other. A
user's single-user server will be at `username.jupyter.mydomain.com`. This also
requires all user subdomains to point to the same address, which is most easily
accomplished with wildcard DNS. Since this spreads the service across multiple
domains, you will need wildcard SSL as well. Unfortunately, for many
institutional domains, wildcard DNS and SSL are not available. **If you do plan
to serve untrusted users, enabling subdomains is highly encouraged**, as it
resolves the cross-site issues.

### Disable user config

If subdomains are unavailable or undesirable, JupyterHub provides a
configuration option `Spawner.disable_user_config`, which can be set to prevent
the user-owned configuration files from being loaded. After implementing this
option, `PATH`s and package installation are the other things that the
admin must enforce.

### Prevent spawners from evaluating shell configuration files

For most Spawners, `PATH` is not something users can influence, but it's important that
the Spawner should _not_ evaluate shell configuration files prior to launching the server.

### Isolate packages using virtualenv

Package isolation is most easily handled by running the single-user server in
a virtualenv with disabled system-site-packages. The user should not have
permission to install packages into this environment.
The same principle extends to the images used by container-based deployments.
If users can select the images in which their servers run, they can disable all security.

It is important to note that the control over the environment only affects the
single-user server, and not the environment(s) in which the user's kernel(s)
may run. Installing additional packages in the kernel environment does not
pose additional risk to the web application's security.

### Encrypt internal connections with SSL/TLS

By default, all communications on the server, between the proxy, hub, and single
-user notebooks are performed unencrypted. Setting the `internal_ssl` flag in
`jupyterhub_config.py` secures the aforementioned routes. Turning this
feature on does require that the enabled `Spawner` can use the certificates
generated by the `Hub` (the default `LocalProcessSpawner` can, for instance).

It is also important to note that this encryption **does not** cover the
`zmq tcp` sockets between the Notebook client and kernel yet. While users cannot
submit arbitrary commands to another user's kernel, they can bind to these
sockets and listen. When serving untrusted users, this eavesdropping can be
mitigated by setting `KernelManager.transport` to `ipc`. This applies standard
Unix permissions to the communication sockets thereby restricting
communication to the socket owner. The `internal_ssl` option will eventually
extend to securing the `tcp` sockets as well.

## Security audits

We recommend that you do periodic reviews of your deployment's security. It's
good practice to keep [JupyterHub](https://readthedocs.org/projects/jupyterhub/), [configurable-http-proxy][], and [nodejs
versions](https://github.com/nodejs/Release) up to date.

A handy website for testing your deployment is
[Qualsys' SSL analyzer tool](https://www.ssllabs.com/ssltest/analyze.html).

[configurable-http-proxy]: https://github.com/jupyterhub/configurable-http-proxy

## Vulnerability reporting

If you believe you have found a security vulnerability in JupyterHub, or any
Jupyter project, please report it to
[security@ipython.org](mailto:security@ipython.org). If you prefer to encrypt
your security reports, you can use [this PGP public
key](https://jupyter.org/assets/ipython_security.asc).