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Metadata-Version: 2.1
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Name: flask-talisman
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Version: 1.1.0
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Summary: HTTP security headers for Flask.
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Home-page: https://github.com/wntrblm/flask-talisman
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Author: Alethea Katherine Flowers
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Author-email: me@thea.codes
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License: Apache Software License
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Keywords: flask security https xss
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Platform: UNKNOWN
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Classifier: Development Status :: 5 - Production/Stable
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Classifier: Intended Audience :: Developers
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Classifier: Topic :: Software Development :: Libraries :: Python Modules
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Classifier: License :: OSI Approved :: Apache Software License
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Classifier: Programming Language :: Python
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Classifier: Programming Language :: Python :: 3
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Classifier: Programming Language :: Python :: 3.5
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Classifier: Programming Language :: Python :: 3.6
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Classifier: Programming Language :: Python :: 3.7
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Classifier: Programming Language :: Python :: 3.8
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Classifier: Programming Language :: Python :: 3.9
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Classifier: Operating System :: POSIX
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Classifier: Operating System :: MacOS
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Classifier: Operating System :: Unix
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License-File: LICENSE
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Talisman: HTTP security headers for Flask
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=========================================
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|PyPI Version|
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Talisman is a small Flask extension that handles setting HTTP headers
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that can help protect against a few common web application security
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issues.
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The default configuration:
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- Forces all connects to ``https``, unless running with debug enabled.
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- Enables `HTTP Strict Transport
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Security <https://developer.mozilla.org/en-US/docs/Web/Security/HTTP_strict_transport_security>`_.
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- Sets Flask's session cookie to ``secure``, so it will never be set if
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your application is somehow accessed via a non-secure connection.
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- Sets Flask's session cookie to ``httponly``, preventing JavaScript
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from being able to access its content. CSRF via Ajax uses a separate
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cookie and should be unaffected.
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- Sets Flask's session cookie to ``Lax``, preventing the cookie to be leaked
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in CSRF-prone request methods.
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- Sets
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`X-Frame-Options <https://developer.mozilla.org/en-US/docs/Web/HTTP/X-Frame-Options>`_
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to ``SAMEORIGIN`` to avoid
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`clickjacking <https://en.wikipedia.org/wiki/Clickjacking>`_.
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- Sets `X-Content-Type-Options
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<https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Content-Type-Options>`_
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to prevent content type sniffing.
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- Sets a strict `Content Security
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Policy <https://developer.mozilla.org/en-US/docs/Web/Security/CSP/Introducing_Content_Security_Policy>`__
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of ``default-src: 'self', 'object-src': 'none'``. This is intended to almost completely
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prevent Cross Site Scripting (XSS) attacks. This is probably the only
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setting that you should reasonably change. See the
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`Content Security Policy`_ section.
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- Sets a strict `Referrer-Policy <https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Referrer-Policy>`_
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of ``strict-origin-when-cross-origin`` that governs which referrer information should be included with
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requests made.
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- Disables ``browsing-topics`` by default in the `Permissions-Policy <https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Feature-Policy>`_
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like `Drupal <https://www.drupal.org/project/drupal/issues/3209628>`_ to enhance privacy protection.
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In addition to Talisman, you **should always use a cross-site request
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forgery (CSRF) library**. It's highly recommended to use
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`Flask-SeaSurf <https://flask-seasurf.readthedocs.org/en/latest/>`_,
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which is based on Django's excellent library.
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Installation & Basic Usage
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--------------------------
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Install via `pip <https://pypi.python.org/pypi/pip>`_:
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::
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pip install flask-talisman
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After installing, wrap your Flask app with a ``Talisman``:
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.. code:: python
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from flask import Flask
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from flask_talisman import Talisman
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app = Flask(__name__)
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Talisman(app)
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There is also a full `Example App <https://github.com/wntrblm/flask-talisman/blob/master/example_app>`_.
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Options
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-------
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- ``force_https``, default ``True``, forces all non-debug connects to
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``https`` (`about HTTPS <https://developer.mozilla.org/en-US/docs/Glossary/https>`_).
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- ``force_https_permanent``, default ``False``, uses ``301`` instead of
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``302`` for ``https`` redirects.
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- ``frame_options``, default ``SAMEORIGIN``, can be ``SAMEORIGIN``,
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``DENY``, or ``ALLOWFROM`` (`about Frame Options <https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Frame-Options>`_).
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- ``frame_options_allow_from``, default ``None``, a string indicating
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the domains that are allowed to embed the site via iframe.
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- ``strict_transport_security``, default ``True``, whether to send HSTS
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headers (`about HSTS <https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Strict-Transport-Security>`_).
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- ``strict_transport_security_preload``, default ``False``, enables HSTS
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preloading. If you register your application with
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`Google's HSTS preload list <https://hstspreload.appspot.com/>`_,
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Firefox and Chrome will never load your site over a non-secure
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connection.
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- ``strict_transport_security_max_age``, default ``ONE_YEAR_IN_SECS``,
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length of time the browser will respect the HSTS header.
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- ``strict_transport_security_include_subdomains``, default ``True``,
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whether subdomains should also use HSTS.
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- ``content_security_policy``, default ``default-src: 'self'`, 'object-src': 'none'``, see the
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`Content Security Policy`_ section (`about Content Security Policy <https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy>`_).
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- ``content_security_policy_nonce_in``, default ``[]``. Adds a per-request nonce
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value to the flask request object and also to the specified CSP header section.
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I.e. ``['script-src', 'style-src']``
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- ``content_security_policy_report_only``, default ``False``, whether to set
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the CSP header as "report-only" (as `Content-Security-Policy-Report-Only`)
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to ease deployment by disabling the policy enforcement by the browser,
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requires passing a value with the ``content_security_policy_report_uri``
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parameter
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- ``content_security_policy_report_uri``, default ``None``, a string
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indicating the report URI used for `CSP violation reports
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<https://developer.mozilla.org/en-US/docs/Web/Security/CSP/Using_CSP_violation_reports>`_
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- ``referrer_policy``, default ``strict-origin-when-cross-origin``, a string
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that sets the Referrer Policy header to send a full URL when performing a same-origin
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request, only send the origin of the document to an equally secure destination
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(HTTPS->HTTPS), and send no header to a less secure destination (HTTPS->HTTP) (`about Referrer Policy <https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Referrer-Policy>`_).
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- ``feature_policy``, default ``{}``, see the `Feature Policy`_ section (`about Feature Policy <https://developer.mozilla.org/en-US/docs/Web/HTTP/Feature_Policy>`_).
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- ``permissions_policy``, default ``{'browsing-topics': '()'}``, see the `Permissions Policy`_ section (`about Permissions Policy <https://developer.mozilla.org/en-US/docs/Web/HTTP/Feature_Policy>`_).
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- ``document_policy``, default ``{}``, see the `Document Policy`_ section (`about Document Policy <https://wicg.github.io/document-policy/>`_).
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- ``session_cookie_secure``, default ``True``, set the session cookie
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to ``secure``, preventing it from being sent over plain ``http`` (`about cookies (https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Set-Cookie)_`).
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- ``session_cookie_http_only``, default ``True``, set the session
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cookie to ``httponly``, preventing it from being read by JavaScript.
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- ``session_cookie_samesite``, default ``Lax``, set this to ``Strict`` to prevent the cookie from being sent by the browser to the target site in all cross-site browsing context, even when following a regular link.
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- ``force_file_save``, default ``False``, whether to set the
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`X-Download-Options <https://docs.microsoft.com/en-us/previous-versions/windows/internet-explorer/ie-developer/compatibility/jj542450(v=vs.85)?redirectedfrom=MSDN>`_
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header to ``noopen`` to prevent IE >= 8 to from opening file downloads
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directly and only save them instead.
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- ``x_content_type_options``, default ``True``, Protects against MIME sniffing vulnerabilities (`about Content Type Options <https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Content-Type-Options>`_).
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- ``x_xss_protection``, default ``False``, Protects against cross-site scripting (XSS) attacks (`about XSS Protection <https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-XSS-Protection>`_). This option is disabled by default because no modern browser (`supports this header <https://caniuse.com/mdn-http_headers_x-xss-protection>`_) anymore.
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For a full list of (security) headers, check out: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers.
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Per-view options
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~~~~~~~~~~~~~~~~
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Sometimes you want to change the policy for a specific view. The
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``force_https``, ``frame_options``, ``frame_options_allow_from``,
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`content_security_policy``, ``feature_policy``, ``permissions_policy``
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and ``document_policy`` options can be changed on a per-view basis.
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.. code:: python
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from flask import Flask
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from flask_talisman import Talisman, ALLOW_FROM
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app = Flask(__name__)
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talisman = Talisman(app)
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@app.route('/normal')
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def normal():
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return 'Normal'
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@app.route('/embeddable')
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@talisman(frame_options=ALLOW_FROM, frame_options_allow_from='*')
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def embeddable():
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return 'Embeddable'
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Content Security Policy
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-----------------------
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The default content security policy is extremely strict and will
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prevent loading any resources that are not in the same domain as the
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application. Most web applications will need to change this policy.
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If you're not ready to deploy Content Security Policy, you can set
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`content_security_policy` to `False` to disable sending this header
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entirely.
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A slightly more permissive policy is available at
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``flask_talisman.GOOGLE_CSP_POLICY``, which allows loading Google-hosted JS
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libraries, fonts, and embeding media from YouTube and Maps.
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You can and should create your own policy to suit your site's needs.
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Here's a few examples adapted from
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`MDN <https://developer.mozilla.org/en-US/docs/Web/Security/CSP/Using_Content_Security_Policy>`_:
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Example 1
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~~~~~~~~~
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This is the default policy. A web site administrator wants all content
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to come from the site's own origin (this excludes subdomains) and disallow
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legacy HTML elements.
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.. code:: python
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csp = {
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'default-src': '\'self\'',
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'object-src': '\'none\'',
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}
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talisman = Talisman(app, content_security_policy=csp)
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Example 2
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~~~~~~~~~
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A web site administrator wants to allow content from a trusted domain
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and all its subdomains (it doesn't have to be the same domain that the
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CSP is set on.)
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.. code:: python
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csp = {
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'default-src': [
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'\'self\'',
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'*.trusted.com'
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]
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}
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Example 3
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~~~~~~~~~
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A web site administrator wants to allow users of a web application to
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include images from any origin in their own content, but to restrict
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audio or video media to trusted providers, and all scripts only to a
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specific server that hosts trusted code.
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.. code:: python
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csp = {
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'default-src': '\'self\'',
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'img-src': '*',
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'media-src': [
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'media1.com',
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'media2.com',
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],
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'script-src': 'userscripts.example.com'
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}
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In this example content is only permitted from the document's origin
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with the following exceptions:
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- Images may loaded from anywhere (note the ``*`` wildcard).
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- Media is only allowed from media1.com and media2.com (and not from
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subdomains of those sites).
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- Executable script is only allowed from userscripts.example.com.
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Example 4
|
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~~~~~~~~~
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A web site administrator for an online banking site wants to ensure that
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all its content is loaded using SSL, in order to prevent attackers from
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eavesdropping on requests.
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.. code:: python
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csp = {
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'default-src': 'https://onlinebanking.jumbobank.com'
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}
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The server only permits access to documents being loaded specifically
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over HTTPS through the single origin onlinebanking.jumbobank.com.
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Example 5
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||||
~~~~~~~~~
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A web site administrator of a web mail site wants to allow HTML in
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email, as well as images loaded from anywhere, but not JavaScript or
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other potentially dangerous content.
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.. code:: python
|
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csp = {
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'default-src': [
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'\'self\'',
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'*.mailsite.com',
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],
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'img-src': '*'
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}
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Note that this example doesn't specify a ``script-src``; with the
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example CSP, this site uses the setting specified by the ``default-src``
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directive, which means that scripts can be loaded only from the
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originating server.
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Example 6
|
||||
~~~~~~~~~
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||||
|
||||
A web site administrator wants to allow embedded scripts (which might
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be generated dynamicially).
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||||
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||||
.. code:: python
|
||||
|
||||
csp = {
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||||
'default-src': '\'self\'',
|
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'script-src': '\'self\'',
|
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}
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talisman = Talisman(
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app,
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content_security_policy=csp,
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||||
content_security_policy_nonce_in=['script-src']
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||||
)
|
||||
|
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The nonce needs to be added to the script tag in the template:
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||||
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||||
.. code:: html
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||||
<script nonce="{{ csp_nonce() }}">
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||||
//...
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||||
</script>
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||||
|
||||
Note that the CSP directive (`script-src` in the example) to which the `nonce-...`
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||||
source should be added needs to be defined explicitly.
|
||||
|
||||
Example 7
|
||||
~~~~~~~~~
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||||
|
||||
A web site adminstrator wants to override the CSP directives via an
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||||
environment variable which doesn't support specifying the policy as
|
||||
a Python dictionary, e.g.:
|
||||
|
||||
.. code:: bash
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||||
|
||||
export CSP_DIRECTIVES="default-src 'self'; image-src *"
|
||||
python app.py
|
||||
|
||||
Then in the app code you can read the CSP directives from the environment:
|
||||
|
||||
.. code:: python
|
||||
|
||||
import os
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||||
from flask_talisman import Talisman, DEFAULT_CSP_POLICY
|
||||
|
||||
talisman = Talisman(
|
||||
app,
|
||||
content_security_policy=os.environ.get("CSP_DIRECTIVES", DEFAULT_CSP_POLICY),
|
||||
)
|
||||
|
||||
As you can see above the policy can be defined simply just like the official
|
||||
specification requires the HTTP header to be set: As a semicolon separated
|
||||
list of individual CSP directives.
|
||||
|
||||
Feature Policy
|
||||
--------------
|
||||
|
||||
**Note:** Feature Policy has largely been `renamed Permissions Policy <https://github.com/w3c/webappsec-feature-policy/issues/359>`_
|
||||
in the latest draft and some features are likely to move to Document Policy.
|
||||
At this writing, most browsers support the ``Feature-Policy`` HTTP Header name.
|
||||
See the `Permissions Policy`_ and `Document Policy`_ sections below should you wish
|
||||
to set these.
|
||||
|
||||
Also note that the Feature Policy specification did not progress beyond the `draft https://wicg.github.io/feature-policy/`
|
||||
stage before being renamed, but is `supported in some form in most browsers
|
||||
<https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Feature-Policy#Browser_compatibility>`_.
|
||||
|
||||
The default feature policy is empty, as this is the default expected behaviour.
|
||||
|
||||
Geolocation Example
|
||||
~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
Disable access to Geolocation interface.
|
||||
|
||||
.. code:: python
|
||||
|
||||
feature_policy = {
|
||||
'geolocation': '\'none\''
|
||||
}
|
||||
talisman = Talisman(app, feature_policy=feature_policy)
|
||||
|
||||
Permissions Policy
|
||||
------------------
|
||||
|
||||
Feature Policy has been split into Permissions Policy and Document Policy but
|
||||
at this writing `browser support of Permissions Policy is very limited <https://caniuse.com/permissions-policy>`_,
|
||||
and it is recommended to still set the ``Feature-Policy`` HTTP Header.
|
||||
Permission Policy support is included in Talisman for when this becomes more
|
||||
widely supported.
|
||||
|
||||
Note that the `Permission Policy is still an Working Draft <https://www.w3.org/TR/permissions-policy/>`_.
|
||||
|
||||
When the same feature or permission is set in both Feature Policy and Permission Policy,
|
||||
the Permission Policy setting will take precedence in browsers that support both.
|
||||
|
||||
It should be noted that the syntax differs between Feature Policy and Permission Policy
|
||||
as can be seen from the ``geolocation`` examples provided.
|
||||
|
||||
The default Permissions Policy is ``browsing-topics=()``, which opts sites out of
|
||||
`Federated Learning of Cohorts <https://wicg.github.io/floc/>`_ an interest-based advertising initiative
|
||||
called Topics API.
|
||||
|
||||
Permission Policy can be set either using a dictionary, or using a string.
|
||||
|
||||
Geolocation and Microphone Example
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
Disable access to Geolocation interface and Microphone using dictionary syntax
|
||||
|
||||
.. code:: python
|
||||
|
||||
permissions_policy = {
|
||||
'geolocation': '()',
|
||||
'microphone': '()'
|
||||
}
|
||||
talisman = Talisman(app, permissions_policy=permissions_policy)
|
||||
|
||||
Disable access to Geolocation interface and Microphone using string syntax
|
||||
|
||||
.. code:: python
|
||||
|
||||
permissions_policy = 'geolocation=(), microphone=()'
|
||||
talisman = Talisman(app, permissions_policy=permissions_policy)
|
||||
|
||||
Document Policy
|
||||
---------------
|
||||
|
||||
Feature Policy has been split into Permissions Policy and Document Policy but
|
||||
at this writing `browser support of Document Policy is very limited <https://caniuse.com/document-policy>`_,
|
||||
and it is recommended to still set the ``Feature-Policy`` HTTP Header.
|
||||
Document Policy support is included in Talisman for when this becomes more
|
||||
widely supported.
|
||||
|
||||
Note that the `Document Policy is still an Unofficial Draft <https://wicg.github.io/document-policy/>`_.
|
||||
|
||||
The default Document Policy is empty, as this is the default expected behaviour.
|
||||
|
||||
Document Policy can be set either using a dictionary, or using a string.
|
||||
|
||||
Oversized-Images Example
|
||||
~~~~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
Forbid oversized-images using dictionary syntax:
|
||||
|
||||
.. code:: python
|
||||
|
||||
document_policy = {
|
||||
'oversized-images': '?0'
|
||||
}
|
||||
talisman = Talisman(app, document_policy=document_policy)
|
||||
|
||||
Forbid oversized-images using string syntax:
|
||||
|
||||
.. code:: python
|
||||
|
||||
document_policy = 'oversized-images=?0'
|
||||
talisman = Talisman(app, document_policy=document_policy)
|
||||
|
||||
Disclaimer
|
||||
----------
|
||||
|
||||
This code originated at Google, but is not an official Google product,
|
||||
experimental or otherwise. It was forked on June 6th, 2021 from the
|
||||
unmaintained GoogleCloudPlatform/flask-talisman.
|
||||
|
||||
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`_
|
||||
|
||||
.. _LICENSE: https://github.com/wntrblm/flask-talisman/blob/master/LICENSE
|
||||
.. _CONTRIBUTING.md: https://github.com/wntrblm/flask-talisman/blob/master/CONTRIBUTING.md
|
||||
.. |PyPI Version| image:: https://img.shields.io/pypi/v/flask-talisman.svg
|
||||
:target: https://pypi.python.org/pypi/flask-talisman
|
||||
|
||||
|
||||
Reference in New Issue
Block a user