Middleware

This document explains all middleware components that come with Django. For information on how to use them and how to write your own middleware, see the middleware usage guide.

Available middleware

Cache middleware

class UpdateCacheMiddleware
class FetchFromCacheMiddleware

Enable the site-wide cache. If these are enabled, each Django-powered page will be cached for as long as the CACHE_MIDDLEWARE_SECONDS setting defines. See the cache documentation.

“Common” middleware

class CommonMiddleware

Adds a few conveniences for perfectionists:

  • Forbids access to user agents in the DISALLOWED_USER_AGENTS setting, which should be a list of compiled regular expression objects.

  • Performs URL rewriting based on the APPEND_SLASH and PREPEND_WWW settings.

    If APPEND_SLASH is True and the initial URL doesn’t end with a slash, and it is not found in the URLconf, then a new URL is formed by appending a slash at the end. If this new URL is found in the URLconf, then Django redirects the request to this new URL. Otherwise, the initial URL is processed as usual.

    For example, foo.com/bar will be redirected to foo.com/bar/ if you don’t have a valid URL pattern for foo.com/bar but do have a valid pattern for foo.com/bar/.

    If PREPEND_WWW is True, URLs that lack a leading “www.” will be redirected to the same URL with a leading “www.”

    Both of these options are meant to normalize URLs. The philosophy is that each URL should exist in one, and only one, place. Technically a URL foo.com/bar is distinct from foo.com/bar/ – a search-engine indexer would treat them as separate URLs – so it’s best practice to normalize URLs.

  • Sets the Content-Length header for non-streaming responses.

CommonMiddleware.response_redirect_class

Defaults to HttpResponsePermanentRedirect. Subclass CommonMiddleware and override the attribute to customize the redirects issued by the middleware.

class BrokenLinkEmailsMiddleware

GZip middleware

class GZipMiddleware

Warning

Security researchers recently revealed that when compression techniques (including GZipMiddleware) are used on a website, the site may become exposed to a number of possible attacks. Before using GZipMiddleware on your site, you should consider very carefully whether you are subject to these attacks. If you’re in any doubt about whether you’re affected, you should avoid using GZipMiddleware. For more details, see the the BREACH paper (PDF) and breachattack.com.

The django.middleware.gzip.GZipMiddleware compresses content for browsers that understand GZip compression (all modern browsers).

This middleware should be placed before any other middleware that need to read or write the response body so that compression happens afterward.

It will NOT compress content if any of the following are true:

  • The content body is less than 200 bytes long.
  • The response has already set the Content-Encoding header.
  • The request (the browser) hasn’t sent an Accept-Encoding header containing gzip.

If the response has an ETag header, the ETag is made weak to comply with RFC 7232#section-2.1.

You can apply GZip compression to individual views using the gzip_page() decorator.

Conditional GET middleware

class ConditionalGetMiddleware

Handles conditional GET operations. If the response doesn’t have an ETag header, the middleware adds one if needed. If the response has an ETag or Last-Modified header, and the request has If-None-Match or If-Modified-Since, the response is replaced by an HttpResponseNotModified.

Locale middleware

class LocaleMiddleware

Enables language selection based on data from the request. It customizes content for each user. See the internationalization documentation.

LocaleMiddleware.response_redirect_class

Defaults to HttpResponseRedirect. Subclass LocaleMiddleware and override the attribute to customize the redirects issued by the middleware.

Message middleware

class MessageMiddleware

Enables cookie- and session-based message support. See the messages documentation.

Security middleware

Warning

If your deployment situation allows, it’s usually a good idea to have your front-end Web server perform the functionality provided by the SecurityMiddleware. That way, if there are requests that aren’t served by Django (such as static media or user-uploaded files), they will have the same protections as requests to your Django application.

class SecurityMiddleware

The django.middleware.security.SecurityMiddleware provides several security enhancements to the request/response cycle. Each one can be independently enabled or disabled with a setting.

HTTP Strict Transport Security

For sites that should only be accessed over HTTPS, you can instruct modern browsers to refuse to connect to your domain name via an insecure connection (for a given period of time) by setting the “Strict-Transport-Security” header. This reduces your exposure to some SSL-stripping man-in-the-middle (MITM) attacks.

SecurityMiddleware will set this header for you on all HTTPS responses if you set the SECURE_HSTS_SECONDS setting to a non-zero integer value.

When enabling HSTS, it’s a good idea to first use a small value for testing, for example, SECURE_HSTS_SECONDS = 3600 for one hour. Each time a Web browser sees the HSTS header from your site, it will refuse to communicate non-securely (using HTTP) with your domain for the given period of time. Once you confirm that all assets are served securely on your site (i.e. HSTS didn’t break anything), it’s a good idea to increase this value so that infrequent visitors will be protected (31536000 seconds, i.e. 1 year, is common).

Additionally, if you set the SECURE_HSTS_INCLUDE_SUBDOMAINS setting to True, SecurityMiddleware will add the includeSubDomains directive to the Strict-Transport-Security header. This is recommended (assuming all subdomains are served exclusively using HTTPS), otherwise your site may still be vulnerable via an insecure connection to a subdomain.

If you wish to submit your site to the browser preload list, set the SECURE_HSTS_PRELOAD setting to True. That appends the preload directive to the Strict-Transport-Security header.

Warning

The HSTS policy applies to your entire domain, not just the URL of the response that you set the header on. Therefore, you should only use it if your entire domain is served via HTTPS only.

Browsers properly respecting the HSTS header will refuse to allow users to bypass warnings and connect to a site with an expired, self-signed, or otherwise invalid SSL certificate. If you use HSTS, make sure your certificates are in good shape and stay that way!

Note

If you are deployed behind a load-balancer or reverse-proxy server, and the Strict-Transport-Security header is not being added to your responses, it may be because Django doesn’t realize that it’s on a secure connection; you may need to set the SECURE_PROXY_SSL_HEADER setting.

Referrer Policy

New in Django 3.0.

Browsers use the Referer header as a way to send information to a site about how users got there. When a user clicks a link, the browser will send the full URL of the linking page as the referrer. While this can be useful for some purposes – like figuring out who’s linking to your site – it also can cause privacy concerns by informing one site that a user was visiting another site.

Some browsers have the ability to accept hints about whether they should send the HTTP Referer header when a user clicks a link; this hint is provided via the Referrer-Policy header. This header can suggest any of three behaviors to browsers:

  • Full URL: send the entire URL in the Referer header. For example, if the user is visiting https://example.com/page.html, the Referer header would contain "https://example.com/page.html".
  • Origin only: send only the “origin” in the referrer. The origin consists of the scheme, host and (optionally) port number. For example, if the user is visiting https://example.com/page.html, the origin would be https://example.com/.
  • No referrer: do not send a Referer header at all.

There are two types of conditions this header can tell a browser to watch out for:

  • Same-origin versus cross-origin: a link from https://example.com/1.html to https://example.com/2.html is same-origin. A link from https://example.com/page.html to https://not.example.com/page.html is cross-origin.
  • Protocol downgrade: a downgrade occurs if the page containing the link is served via HTTPS, but the page being linked to is not served via HTTPS.

Warning

When your site is served via HTTPS, Django’s CSRF protection system requires the Referer header to be present, so completely disabling the Referer header will interfere with CSRF protection. To gain most of the benefits of disabling Referer headers while also keeping CSRF protection, consider enabling only same-origin referrers.

SecurityMiddleware can set the Referrer-Policy header for you, based on the SECURE_REFERRER_POLICY setting (note spelling: browsers send a Referer header when a user clicks a link, but the header instructing a browser whether to do so is spelled Referrer-Policy). The valid values for this setting are:

no-referrer
Instructs the browser to send no referrer for links clicked on this site.
no-referrer-when-downgrade
Instructs the browser to send a full URL as the referrer, but only when no protocol downgrade occurs.
origin
Instructs the browser to send only the origin, not the full URL, as the referrer.
origin-when-cross-origin
Instructs the browser to send the full URL as the referrer for same-origin links, and only the origin for cross-origin links.
same-origin
Instructs the browser to send a full URL, but only for same-origin links. No referrer will be sent for cross-origin links.
strict-origin
Instructs the browser to send only the origin, not the full URL, and to send no referrer when a protocol downgrade occurs.
strict-origin-when-cross-origin
Instructs the browser to send the full URL when the link is same-origin and no protocol downgrade occurs; send only the origin when the link is cross-origin and no protocol downgrade occurs; and no referrer when a protocol downgrade occurs.
unsafe-url
Instructs the browser to always send the full URL as the referrer.

Unknown Policy Values

Where a policy value is unknown by a user agent, it is possible to specify multiple policy values to provide a fallback. The last specified value that is understood takes precedence. To support this, an iterable or comma-separated string can be used with SECURE_REFERRER_POLICY.

X-Content-Type-Options: nosniff

Some browsers will try to guess the content types of the assets that they fetch, overriding the Content-Type header. While this can help display sites with improperly configured servers, it can also pose a security risk.

If your site serves user-uploaded files, a malicious user could upload a specially-crafted file that would be interpreted as HTML or JavaScript by the browser when you expected it to be something harmless.

To prevent the browser from guessing the content type and force it to always use the type provided in the Content-Type header, you can pass the X-Content-Type-Options: nosniff header. SecurityMiddleware will do this for all responses if the SECURE_CONTENT_TYPE_NOSNIFF setting is True.

Note that in most deployment situations where Django isn’t involved in serving user-uploaded files, this setting won’t help you. For example, if your MEDIA_URL is served directly by your front-end Web server (nginx, Apache, etc.) then you’d want to set this header there. On the other hand, if you are using Django to do something like require authorization in order to download files and you cannot set the header using your Web server, this setting will be useful.

X-XSS-Protection: 1; mode=block

Some browsers have the ability to block content that appears to be an XSS attack. They work by looking for JavaScript content in the GET or POST parameters of a page. If the JavaScript is replayed in the server’s response, the page is blocked from rendering and an error page is shown instead.

The X-XSS-Protection header is used to control the operation of the XSS filter.

To enable the XSS filter in the browser, and force it to always block suspected XSS attacks, you can pass the X-XSS-Protection: 1; mode=block header. SecurityMiddleware will do this for all responses if the SECURE_BROWSER_XSS_FILTER setting is True.

Warning

The browser XSS filter is a useful defense measure, but must not be relied upon exclusively. It cannot detect all XSS attacks and not all browsers support the header. Ensure you are still validating and sanitizing all input to prevent XSS attacks.

SSL Redirect

If your site offers both HTTP and HTTPS connections, most users will end up with an unsecured connection by default. For best security, you should redirect all HTTP connections to HTTPS.

If you set the SECURE_SSL_REDIRECT setting to True, SecurityMiddleware will permanently (HTTP 301) redirect all HTTP connections to HTTPS.

Note

For performance reasons, it’s preferable to do these redirects outside of Django, in a front-end load balancer or reverse-proxy server such as nginx. SECURE_SSL_REDIRECT is intended for the deployment situations where this isn’t an option.

If the SECURE_SSL_HOST setting has a value, all redirects will be sent to that host instead of the originally-requested host.

If there are a few pages on your site that should be available over HTTP, and not redirected to HTTPS, you can list regular expressions to match those URLs in the SECURE_REDIRECT_EXEMPT setting.

Note

If you are deployed behind a load-balancer or reverse-proxy server and Django can’t seem to tell when a request actually is already secure, you may need to set the SECURE_PROXY_SSL_HEADER setting.

Session middleware

class SessionMiddleware

Enables session support. See the session documentation.

Site middleware

class CurrentSiteMiddleware

Adds the site attribute representing the current site to every incoming HttpRequest object. See the sites documentation.

Authentication middleware

class AuthenticationMiddleware

Adds the user attribute, representing the currently-logged-in user, to every incoming HttpRequest object. See Authentication in Web requests.

class RemoteUserMiddleware

Middleware for utilizing Web server provided authentication. See Authentication using REMOTE_USER for usage details.

class PersistentRemoteUserMiddleware

Middleware for utilizing Web server provided authentication when enabled only on the login page. See Using REMOTE_USER on login pages only for usage details.

CSRF protection middleware

class CsrfViewMiddleware

Adds protection against Cross Site Request Forgeries by adding hidden form fields to POST forms and checking requests for the correct value. See the Cross Site Request Forgery protection documentation.

X-Frame-Options middleware

class XFrameOptionsMiddleware

Simple clickjacking protection via the X-Frame-Options header.

Middleware ordering

Here are some hints about the ordering of various Django middleware classes:

  1. SecurityMiddleware

    It should go near the top of the list if you’re going to turn on the SSL redirect as that avoids running through a bunch of other unnecessary middleware.

  2. UpdateCacheMiddleware

    Before those that modify the Vary header (SessionMiddleware, GZipMiddleware, LocaleMiddleware).

  3. GZipMiddleware

    Before any middleware that may change or use the response body.

    After UpdateCacheMiddleware: Modifies Vary header.

  4. SessionMiddleware

    Before any middleware that may raise an exception to trigger an error view (such as PermissionDenied) if you’re using CSRF_USE_SESSIONS.

    After UpdateCacheMiddleware: Modifies Vary header.

  5. ConditionalGetMiddleware

    Before any middleware that may change the response (it sets the ETag header).

    After GZipMiddleware so it won’t calculate an ETag header on gzipped contents.

  6. LocaleMiddleware

    One of the topmost, after SessionMiddleware (uses session data) and UpdateCacheMiddleware (modifies Vary header).

  7. CommonMiddleware

    Before any middleware that may change the response (it sets the Content-Length header). A middleware that appears before CommonMiddleware and changes the response must reset Content-Length.

    Close to the top: it redirects when APPEND_SLASH or PREPEND_WWW are set to True.

    After SessionMiddleware if you’re using CSRF_USE_SESSIONS.

  8. CsrfViewMiddleware

    Before any view middleware that assumes that CSRF attacks have been dealt with.

    Before RemoteUserMiddleware, or any other authentication middleware that may perform a login, and hence rotate the CSRF token, before calling down the middleware chain.

    After SessionMiddleware if you’re using CSRF_USE_SESSIONS.

  9. AuthenticationMiddleware

    After SessionMiddleware: uses session storage.

  10. MessageMiddleware

    After SessionMiddleware: can use session-based storage.

  11. FetchFromCacheMiddleware

    After any middleware that modifies the Vary header: that header is used to pick a value for the cache hash-key.

  12. FlatpageFallbackMiddleware

    Should be near the bottom as it’s a last-resort type of middleware.

  13. RedirectFallbackMiddleware

    Should be near the bottom as it’s a last-resort type of middleware.

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