# 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 is not necessarily unsuitable for serving untrusted users.

Using JupyterHub with untrusted users does mean more work by the administrator. Much care is required to secure a Hub, with extra caution on protecting users from each other as the Hub is serving untrusted users.

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. 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. JupyterHub’s authentication setup prevents a user writing arbitrary HTML and serving it to another user 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:

• A user may not install new packages in the Python environment that runs their single-user server.

• If the PATH is used to resolve the single-user executable (instead of using an absolute path), a user may not create new files in any PATH directory that precedes the directory containing jupyterhub-singleuser.

• A user may not modify environment variables (e.g. PATH, PYTHONPATH) for their single-user server.

• A user may not modify the configuration of the notebook server (the ~/.jupyter or JUPYTER_CONFIG_DIR directory).

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¶

Several approaches to mitigating these 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 not available or not desirable, 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, PATHs and package installation and PATHs 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 care should be taken to ensure that the Spawner does 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.

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 communication on the server, between the proxy, hub, and single -user notebooks is 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 (yet) cover the zmq tcp sockets between the Notebook client and kernel. 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, configurable-http-proxy, and nodejs versions up to date.

A handy website for testing your deployment is Qualsys’ SSL analyzer tool.

## Vulnerability reporting¶

If you believe you’ve found a security vulnerability in JupyterHub, or any Jupyter project, please report it to security@ipython.org. If you prefer to encrypt your security reports, you can use this PGP public key.