Django documentation

Security in Django

This document is an overview of Django’s security features. It includes advice on securing a Django-powered site.

Cross site scripting (XSS) protection

XSS attacks allow a user to inject client side scripts into the browsers of other users. This is usually achieved by storing the malicious scripts in the database where it will be retrieved and displayed to other users, or by getting users to click a link which will cause the attacker’s JavaScript to be executed by the user’s browser. However, XSS attacks can originate from any untrusted source of data, such as cookies or Web services, whenever the data is not sufficiently sanitized before including in a page.

Using Django templates protects you against the majority of XSS attacks. However, it is important to understand what protections it provides and its limitations.

Django templates escape specific characters which are particularly dangerous to HTML. While this protects users from most malicious input, it is not entirely foolproof. For example, it will not protect the following:

<style class={{ var }}>...</style>

If var is set to 'class1 onmouseover=javascript:func()', this can result in unauthorized JavaScript execution, depending on how the browser renders imperfect HTML.

It is also important to be particularly careful when using is_safe with custom template tags, the safe template tag, mark_safe, and when autoescape is turned off.

In addition, if you are using the template system to output something other than HTML, there may be entirely separate characters and words which require escaping.

You should also be very careful when storing HTML in the database, especially when that HTML is retrieved and displayed.

Markup library

If you use django.contrib.markup, you need to ensure that the filters are only used on trusted input, or that you have correctly configured them to ensure they do not allow raw HTML output. See the documentation of that module for more information.

Cross site request forgery (CSRF) protection

CSRF attacks allow a malicious user to execute actions using the credentials of another user without that user’s knowledge or consent.

Django has built-in protection against most types of CSRF attacks, providing you have enabled and used it where appropriate. However, as with any mitigation technique, there are limitations. For example, it is possible to disable the CSRF module globally or for particular views. You should only do this if you know what you are doing. There are other limitations if your site has subdomains that are outside of your control.

CSRF protection works by checking for a nonce in each POST request. This ensures that a malicious user cannot simply “replay” a form POST to your Web site and have another logged in user unwittingly submit that form. The malicious user would have to know the nonce, which is user specific (using a cookie).

Be very careful with marking views with the csrf_exempt decorator unless it is absolutely necessary.

SQL injection protection

SQL injection is a type of attack where a malicious user is able to execute arbitrary SQL code on a database. This can result in records being deleted or data leakage.

By using Django’s querysets, the resulting SQL will be properly escaped by the underlying database driver. However, Django also gives developers power to write raw queries or execute custom sql. These capabilities should be used sparingly and you should always be careful to properly escape any parameters that the user can control. In addition, you should exercise caution when using extra().

Clickjacking protection

Clickjacking is a type of attack where a malicious site wraps another site in a frame. This attack can result in an unsuspecting user being tricked into performing unintended actions on the target site.

Django contains clickjacking protection in the form of the X-Frame-Options middleware which in a supporting browser can prevent a site from being rendered inside a frame. It is possible to disable the protection on a per view basis or to configure the exact header value sent.

The middleware is strongly recommended for any site that does not need to have its pages wrapped in a frame by third party sites, or only needs to allow that for a small section of the site.

SSL/HTTPS

It is always better for security, though not always practical in all cases, to deploy your site behind HTTPS. Without this, it is possible for malicious network users to sniff authentication credentials or any other information transferred between client and server, and in some cases – active network attackers – to alter data that is sent in either direction.

If you want the protection that HTTPS provides, and have enabled it on your server, there are some additional steps you may need:

  • If necessary, set SECURE_PROXY_SSL_HEADER, ensuring that you have understood the warnings there thoroughly. Failure to do this can result in CSRF vulnerabilities, and failure to do it correctly can also be dangerous!

  • Set up redirection so that requests over HTTP are redirected to HTTPS.

    This could be done using a custom middleware. Please note the caveats under SECURE_PROXY_SSL_HEADER. For the case of a reverse proxy, it may be easier or more secure to configure the main Web server to do the redirect to HTTPS.

  • Use ‘secure’ cookies.

    If a browser connects initially via HTTP, which is the default for most browsers, it is possible for existing cookies to be leaked. For this reason, you should set your SESSION_COOKIE_SECURE and CSRF_COOKIE_SECURE settings to True. This instructs the browser to only send these cookies over HTTPS connections. Note that this will mean that sessions will not work over HTTP, and the CSRF protection will prevent any POST data being accepted over HTTP (which will be fine if you are redirecting all HTTP traffic to HTTPS).

Host header validation

Django uses the Host header provided by the client to construct URLs in certain cases. While these values are sanitized to prevent Cross Site Scripting attacks, a fake Host value can be used for Cross-Site Request Forgery, cache poisoning attacks, and poisoning links in emails.

Because even seemingly-secure webserver configurations are susceptible to fake Host headers, Django validates Host headers against the ALLOWED_HOSTS setting in the django.http.HttpRequest.get_host() method.

This validation only applies via get_host(); if your code accesses the Host header directly from request.META you are bypassing this security protection.

For more details see the full ALLOWED_HOSTS documentation.

Warning

Previous versions of this document recommended configuring your webserver to ensure it validates incoming HTTP Host headers. While this is still recommended, in many common webservers a configuration that seems to validate the Host header may not in fact do so. For instance, even if Apache is configured such that your Django site is served from a non-default virtual host with the ServerName set, it is still possible for an HTTP request to match this virtual host and supply a fake Host header. Thus, Django now requires that you set ALLOWED_HOSTS explicitly rather than relying on webserver configuration.

Additionally, as of 1.3.1, Django requires you to explicitly enable support for the X-Forwarded-Host header (via the USE_X_FORWARDED_HOST setting) if your configuration requires it.

Additional security topics

While Django provides good security protection out of the box, it is still important to properly deploy your application and take advantage of the security protection of the Web server, operating system and other components.

  • Make sure that your Python code is outside of the Web server’s root. This will ensure that your Python code is not accidentally served as plain text (or accidentally executed).
  • Take care with any user uploaded files.
  • Django does not throttle requests to authenticate users. To protect against brute-force attacks against the authentication system, you may consider deploying a Django plugin or Web server module to throttle these requests.
  • If your site accepts file uploads, it is strongly advised that you limit these uploads in your Web server configuration to a reasonable size in order to prevent denial of service (DOS) attacks. In Apache, this can be easily set using the LimitRequestBody directive.
  • Keep your SECRET_KEY a secret.
  • It is a good idea to limit the accessibility of your caching system and database using a firewall.

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