flask-talisman 0.6.0

Installation & Basic Usage

Install via pip:

pip install flask-talisman

After installing, wrap your Flask app with a Talisman:

from flask import Flask
from flask_talisman import Talisman

app = Flask(__name__)
Talisman(app)

There is also a full Example App.

Options

• feature_policy, default {}, see the Feature Policy section.

• force_https, default True, forces all non-debug connects to https.

• force_https_permanent, default False, uses 301 instead of 302 for https redirects.

• frame_options, default SAMEORIGIN, can be SAMEORIGIN, DENY, or ALLOWFROM.

• frame_options_allow_from, default None, a string indicating the domains that are allowed to embed the site via iframe.

• strict_transport_security, default True, whether to send HSTS headers.

• strict_transport_security_preload, default False, enables HSTS preloading If you register your application with Google’s HSTS preload list, Firefox and Chrome will never load your site over a non-secure connection.

• strict_transport_security_max_age, default ONE_YEAR_IN_SECS, length of time the browser will respect the HSTS header.

• strict_transport_security_include_subdomains, default True, whether subdomains should also use HSTS.

• content_security_policy, default default-src: 'self', see the Content Security Policy section.

• content_security_policy_nonce_in, default []. Adds a per-request nonce

  value to the flask request object and also to the specified CSP header section. I.e. [‘script-src’, ‘style-src’]

• content_security_policy_report_only, default False, whether to set the CSP header as “report-only” (as Content-Security-Policy-Report-Only) to ease deployment by disabling the policy enforcement by the browser, requires passing a value with the content_security_policy_report_uri parameter

• content_security_policy_report_uri, default None, a string indicating the report URI used for CSP violation reports

• referrer_policy, default strict-origin-when-cross-origin, a string that sets the Referrer Policy header to send a full URL when performing a same-origin request, only send the origin of the document to an equally secure destination (HTTPS->HTTPS), and send no header to a less secure destination (HTTPS->HTTP).

• session_cookie_secure, default True, set the session cookie to secure, preventing it from being sent over plain http.

• session_cookie_http_only, default True, set the session cookie to httponly, preventing it from being read by JavaScript.

• force_file_save, default False, whether to set the X-Download-Options header to noopen to prevent IE >= 8 to from opening file downloads directly and only save them instead

from flask import Flask
from flask_talisman import Talisman, ALLOW_FROM

app = Flask(__name__)
talisman = Talisman(app)

@app.route('/normal')
def normal():
    return 'Normal'

@app.route('/embeddable')
@talisman(frame_options=ALLOW_FROM, frame_options_allow_from='*')
def embeddable():
    return 'Embeddable'

Content Security Policy

The default content security policy is extremely strict and will prevent loading any resources that are not in the same domain as the application. Most web applications will need to change this policy.

A slightly more permissive policy is available at flask_talisman.GOOGLE_CSP_POLICY, which allows loading Google-hosted JS libraries, fonts, and embeding media from YouTube and Maps.

You can and should create your own policy to suit your site’s needs. Here’s a few examples adapted from MDN:

csp = {
    'default-src': '\'self\''
}
talisman = Talisman(app, content_security_policy=csp)

csp = {
    'default-src': [
        '\'self\'',
        '*.trusted.com'
    ]
}

csp = {
    'default-src': '\'self\'',
    'img-src': '*',
    'media-src': [
        'media1.com',
        'media2.com',
    ],
    'script-src': 'userscripts.example.com'
}

csp = {
    'default-src': 'https://onlinebanking.jumbobank.com'
}

csp = {
    'default-src': [
        '\'self\'',
        '*.mailsite.com',
    ],
    'img-src': '*'
}

csp = {
    'default-src': '\'self\'',
    'script-src': '\'self\'',
}
talisman = Talisman(
    app,
    content_security_policy=csp,
    content_security_policy_nonce_in=['script-src']
)

<script nonce="{{ csp_nonce() }}">
    //...
</script>

Feature Policy

The default feature policy is empty, as this is the default expected behaviour. Note that the Feature Policy is still a draft https://wicg.github.io/feature-policy/ and supported in Chrome and Safari.

feature_policy = {
    'geolocation': '\'none\''
}
talisman = Talisman(app, feature_policy=feature_policy)

Disclaimer

This is not an official Google product, experimental or otherwise.

There is no silver bullet for web application security. Talisman can help, but security is more than just setting a few headers. Any public-facing web application should have a comprehensive approach to security.

Contributing changes

• See CONTRIBUTING.md

Licensing

• Apache 2.0 - See LICENSE