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¶
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¶
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
andPREPEND_WWW
settings.If
APPEND_SLASH
isTrue
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 tofoo.com/bar/
if you don’t have a valid URL pattern forfoo.com/bar
but do have a valid pattern forfoo.com/bar/
.If
PREPEND_WWW
isTrue
, 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 fromfoo.com/bar/
– a search-engine indexer would treat them as separate URLs – so it’s best practice to normalize URLs.If necessary, individual views may be excluded from the
APPEND_SLASH
behavior using theno_append_slash()
decorator:from django.views.decorators.common import no_append_slash @no_append_slash def sensitive_fbv(request, *args, **kwargs): """View to be excluded from APPEND_SLASH.""" return HttpResponse()
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.
- Sends broken link notification emails to
MANAGERS
(see How to manage error reporting).
GZip middleware¶
-
class
GZipMiddleware
[source]¶ -
max_random_bytes
¶ Defaults to 100. Subclass
GZipMiddleware
and override the attribute to change the maximum number of random bytes that is included with compressed responses.
-
Note
Security researchers revealed that when compression techniques (including
GZipMiddleware
) are used on a website, the site may become exposed to a
number of possible attacks.
To mitigate attacks, Django implements a technique called Heal The Breach
(HTB). It adds up to 100 bytes (see
max_random_bytes
) of random bytes to each response
to make the attacks less effective.
For more details, see the BREACH paper (PDF), breachattack.com, and the Heal The Breach (HTB) paper.
Mitigation for the BREACH attack was added.
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 containinggzip
.
If the response has an ETag
header, the ETag is made weak to comply with
RFC 9110#section-8.8.1.
You can apply GZip compression to individual views using the
gzip_page()
decorator.
Conditional GET middleware¶
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¶
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¶
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.
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.
SECURE_CONTENT_TYPE_NOSNIFF
SECURE_CROSS_ORIGIN_OPENER_POLICY
SECURE_HSTS_INCLUDE_SUBDOMAINS
SECURE_HSTS_PRELOAD
SECURE_HSTS_SECONDS
SECURE_REDIRECT_EXEMPT
SECURE_REFERRER_POLICY
SECURE_SSL_HOST
SECURE_SSL_REDIRECT
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¶
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 visitinghttps://example.com/page.html
, theReferer
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 behttps://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
tohttps://example.com/2.html
is same-origin. A link fromhttps://example.com/page.html
tohttps://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
.
Cross-Origin Opener Policy¶
Some browsers have the ability to isolate top-level windows from other
documents by putting them in a separate browsing context group based on the
value of the Cross-Origin Opener Policy (COOP) header. If a document that
is isolated in this way opens a cross-origin popup window, the popup’s
window.opener
property will be null
. Isolating windows using COOP is a
defense-in-depth protection against cross-origin attacks, especially those like
Spectre which allowed exfiltration of data loaded into a shared browsing
context.
SecurityMiddleware
can set the Cross-Origin-Opener-Policy
header for
you, based on the SECURE_CROSS_ORIGIN_OPENER_POLICY
setting. The
valid values for this setting are:
same-origin
- Isolates the browsing context exclusively to same-origin documents. Cross-origin documents are not loaded in the same browsing context. This is the default and most secure option.
same-origin-allow-popups
- Isolates the browsing context to same-origin documents or those which
either don’t set COOP or which opt out of isolation by setting a COOP of
unsafe-none
. unsafe-none
- Allows the document to be added to its opener’s browsing context group
unless the opener itself has a COOP of
same-origin
orsame-origin-allow-popups
.
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.
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¶
Enables session support. See the session documentation.
Site middleware¶
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 How to authenticate 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¶
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¶
Simple clickjacking protection via the X-Frame-Options header.
Middleware ordering¶
Here are some hints about the ordering of various Django middleware classes:
-
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.
-
Before those that modify the
Vary
header (SessionMiddleware
,GZipMiddleware
,LocaleMiddleware
). -
Before any middleware that may change or use the response body.
After
UpdateCacheMiddleware
: ModifiesVary
header. -
Before any middleware that may raise an exception to trigger an error view (such as
PermissionDenied
) if you’re usingCSRF_USE_SESSIONS
.After
UpdateCacheMiddleware
: ModifiesVary
header. -
Before any middleware that may change the response (it sets the
ETag
header).After
GZipMiddleware
so it won’t calculate anETag
header on gzipped contents. -
One of the topmost, after
SessionMiddleware
(uses session data) andUpdateCacheMiddleware
(modifiesVary
header). -
Before any middleware that may change the response (it sets the
Content-Length
header). A middleware that appears beforeCommonMiddleware
and changes the response must resetContent-Length
.Close to the top: it redirects when
APPEND_SLASH
orPREPEND_WWW
are set toTrue
.After
SessionMiddleware
if you’re usingCSRF_USE_SESSIONS
. -
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 usingCSRF_USE_SESSIONS
. -
After
SessionMiddleware
: uses session storage. -
After
SessionMiddleware
: can use session-based storage. -
After any middleware that modifies the
Vary
header: that header is used to pick a value for the cache hash-key. -
Should be near the bottom as it’s a last-resort type of middleware.
-
Should be near the bottom as it’s a last-resort type of middleware.