Security in the Jupyter notebook server

Since access to the Jupyter notebook server means access to running arbitrary code, it is important to restrict access to the notebook server. For this reason, notebook 4.3 introduces token-based authentication that is on by default.

Note

If you enable a password for your notebook server, token authentication is not enabled by default, and the behavior of the notebook server is unchanged from from versions earlier than 4.3.

When token authentication is enabled, the notebook uses a token to authenticate requests. This token can be provided to login to the notebook server in three ways:

  • in the Authorization header, e.g.:

    Authorization: token abcdef...

  • In a URL parameter, e.g.:

    https://my-notebook/tree/?token=abcdef...

  • In the password field of the login form that will be shown to you if you are not logged in.

When you start a notebook server with token authentication enabled (default), a token is generated to use for authentication. This token is logged to the terminal, so that you can copy/paste the URL into your browser:

[I 11:59:16.597 NotebookApp] The Jupyter Notebook is running at: http://localhost:8888/?token=c8de56fa4deed24899803e93c227592aef6538f93025fe01

If the notebook server is going to open your browser automatically (the default, unless --no-browser has been passed), an additional token is generated for launching the browser. This additional token can be used only once, and is used to set a cookie for your browser once it connects. After your browser has made its first request with this one-time-token, the token is discarded and a cookie is set in your browser.

At any later time, you can see the tokens and URLs for all of your running servers with jupyter notebook list:

$ jupyter notebook list
Currently running servers:
http://localhost:8888/?token=abc... :: /home/you/notebooks
https://0.0.0.0:9999/?token=123... :: /tmp/public
http://localhost:8889/ :: /tmp/has-password

For servers with token-authentication enabled, the URL in the above listing will include the token, so you can copy and paste that URL into your browser to login. If a server has no token (e.g. it has a password or has authentication disabled), the URL will not include the token argument. Once you have visited this URL, a cookie will be set in your browser and you won’t need to use the token again, unless you switch browsers, clear your cookies, or start a notebook server on a new port.

You can disable authentication altogether by setting the token and password to empty strings, but this is NOT RECOMMENDED, unless authentication or access restrictions are handled at a different layer in your web application:

c.NotebookApp.token = ''
c.NotebookApp.password = ''

Security in notebook documents

As Jupyter notebooks become more popular for sharing and collaboration, the potential for malicious people to attempt to exploit the notebook for their nefarious purposes increases. IPython 2.0 introduced a security model to prevent execution of untrusted code without explicit user input.

The problem

The whole point of Jupyter is arbitrary code execution. We have no desire to limit what can be done with a notebook, which would negatively impact its utility.

Unlike other programs, a Jupyter notebook document includes output. Unlike other documents, that output exists in a context that can execute code (via Javascript).

The security problem we need to solve is that no code should execute just because a user has opened a notebook that they did not write. Like any other program, once a user decides to execute code in a notebook, it is considered trusted, and should be allowed to do anything.

Our security model

  • Untrusted HTML is always sanitized
  • Untrusted Javascript is never executed
  • HTML and Javascript in Markdown cells are never trusted
  • Outputs generated by the user are trusted
  • Any other HTML or Javascript (in Markdown cells, output generated by others) is never trusted
  • The central question of trust is “Did the current user do this?”

The details of trust

When a notebook is executed and saved, a signature is computed from a digest of the notebook’s contents plus a secret key. This is stored in a database, writable only by the current user. By default, this is located at:

~/.local/share/jupyter/nbsignatures.db  # Linux
~/Library/Jupyter/nbsignatures.db       # OS X
%APPDATA%/jupyter/nbsignatures.db       # Windows

Each signature represents a series of outputs which were produced by code the current user executed, and are therefore trusted.

When you open a notebook, the server computes its signature, and checks if it’s in the database. If a match is found, HTML and Javascript output in the notebook will be trusted at load, otherwise it will be untrusted.

Any output generated during an interactive session is trusted.

Updating trust

A notebook’s trust is updated when the notebook is saved. If there are any untrusted outputs still in the notebook, the notebook will not be trusted, and no signature will be stored. If all untrusted outputs have been removed (either via Clear Output or re-execution), then the notebook will become trusted.

While trust is updated per output, this is only for the duration of a single session. A newly loaded notebook file is either trusted or not in its entirety.

Explicit trust

Sometimes re-executing a notebook to generate trusted output is not an option, either because dependencies are unavailable, or it would take a long time. Users can explicitly trust a notebook in two ways:

  • At the command-line, with:

    jupyter trust /path/to/notebook.ipynb

  • After loading the untrusted notebook, with File / Trust Notebook

These two methods simply load the notebook, compute a new signature, and add that signature to the user’s database.

Reporting security issues

If you find a security vulnerability in Jupyter, either a failure of the code to properly implement the model described here, or a failure of the model itself, please report it to security@ipython.org.

If you prefer to encrypt your security reports, you can use this PGP public key.

Affected use cases

Some use cases that work in Jupyter 1.0 became less convenient in 2.0 as a result of the security changes. We do our best to minimize these annoyances, but security is always at odds with convenience.

Javascript and CSS in Markdown cells

While never officially supported, it had become common practice to put hidden Javascript or CSS styling in Markdown cells, so that they would not be visible on the page. Since Markdown cells are now sanitized (by Google Caja), all Javascript (including click event handlers, etc.) and CSS will be stripped.

We plan to provide a mechanism for notebook themes, but in the meantime styling the notebook can only be done via either custom.css or CSS in HTML output. The latter only have an effect if the notebook is trusted, because otherwise the output will be sanitized just like Markdown.

Collaboration

When collaborating on a notebook, people probably want to see the outputs produced by their colleagues’ most recent executions. Since each collaborator’s key will differ, this will result in each share starting in an untrusted state. There are three basic approaches to this:

  • re-run notebooks when you get them (not always viable)
  • explicitly trust notebooks via jupyter trust or the notebook menu (annoying, but easy)
  • share a notebook signatures database, and use configuration dedicated to the collaboration while working on the project.

To share a signatures database among users, you can configure:

c.NotebookNotary.data_dir = "/path/to/signature_dir"

to specify a non-default path to the SQLite database (of notebook hashes, essentially). We are aware that SQLite doesn’t work well on NFS and we are working out better ways to do this.