Strict-Transport-Security response header (often
abbreviated as HSTS) lets a web site tell browsers that it should only
be accessed using HTTPS, instead of using HTTP.
|Header type||Response header|
|Forbidden header name||no|
Strict-Transport-Security: max-age=<expire-time> Strict-Transport-Security: max-age=<expire-time>; includeSubDomains Strict-Transport-Security: max-age=<expire-time>; preload
The time, in seconds, that the browser should remember that a site is only to be accessed using HTTPS.
If this optional parameter is specified, this rule applies to all of the site's subdomains as well.
See Preloading Strict Transport Security for details. Not part of the specification.
If a website accepts a connection through HTTP and redirects to HTTPS, visitors may initially communicate with the non-encrypted version of the site before being redirected, if, for example, the visitor types http://www.foo.com/ or even just foo.com. This creates an opportunity for a man-in-the-middle attack. The redirect could be exploited to direct visitors to a malicious site instead of the secure version of the original site.
The HTTP Strict Transport Security header informs the browser that it should never load a site using HTTP and should automatically convert all attempts to access the site using HTTP to HTTPS requests instead.
is ignored by the browser when your site is accessed using HTTP; this
is because an attacker may intercept HTTP connections and inject the header or remove
it. When your site is accessed over HTTPS with no certificate errors, the browser knows
your site is HTTPS capable and will honor the
You log into a free WiFi access point at an airport and start surfing the web, visiting your online banking service to check your balance and pay a couple of bills. Unfortunately, the access point you're using is actually a hacker's laptop, and they're intercepting your original HTTP request and redirecting you to a clone of your bank's site instead of the real thing. Now your private data is exposed to the hacker.
Strict Transport Security resolves this problem; as long as you've accessed your bank's web site once using HTTPS, and the bank's web site uses Strict Transport Security, your browser will know to automatically use only HTTPS, which prevents hackers from performing this sort of man-in-the-middle attack.
The first time your site is accessed using HTTPS and it returns the
Strict-Transport-Security header, the browser records this information, so
that future attempts to load the site using HTTP will automatically use HTTPS instead.
When the expiration time specified by the Strict-Transport-Security header elapses, the next attempt to load the site via HTTP will proceed as normal instead of automatically using HTTPS.
Whenever the Strict-Transport-Security header is delivered to the browser, it will
update the expiration time for that site, so sites can refresh this information and
prevent the timeout from expiring. Should it be necessary to disable Strict Transport
Security, setting the max-age to 0 (over an https connection) will immediately expire the
Strict-Transport-Security header, allowing access via http.
Google maintains an HSTS preload service. By following the guidelines and successfully submitting your domain, browsers will never connect to your domain using an insecure connection. While the service is hosted by Google, all browsers have stated an intent to use (or actually started using) the preload list. However, it is not part of the HSTS specification and should not be treated as official.
All present and future subdomains will be HTTPS for a
max-age of 1 year. This blocks
access to pages or subdomains that can only be served over HTTP.
Strict-Transport-Security: max-age=31536000; includeSubDomains
max-age of 1 year is acceptable for a domain,
however, two years is the recommended value as explained on https://hstspreload.org.
In the following example,
max-age is set to 2 years, and is suffixed with
preload, which is necessary for inclusion in most major web browsers' HSTS
preload lists, like Chromium, Edge, and Firefox.
Strict-Transport-Security: max-age=63072000; includeSubDomains; preload
|HTTP Strict Transport Security (HSTS) (HSTS)|
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