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Difference between revisions of "HTTP Strict Transport Security"
(add caniuse.com) |
(Added Excessively Strict STS note. Changed HSTS upgraded to redirects.) |
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Strict-Transport-Security: max-age=31536000; includeSubDomains | Strict-Transport-Security: max-age=31536000; includeSubDomains | ||
| + | |||
| + | == Excessively Strict STS == | ||
| + | |||
| + | Use caution when setting excessively strict STS policies. Including subdomains should only be used in environments where all sites within your organization for the given domain name require ssl. Max-age limits should be carefully considered as infrequent visitors may find your site inaccessible if you relax your policy. | ||
== Browser Support == | == Browser Support == | ||
| Line 72: | Line 76: | ||
HSTS addresses the following threats: | HSTS addresses the following threats: | ||
* User bookmarks or manually types http://example.com and is subject to a man-in-the-middle attacker | * User bookmarks or manually types http://example.com and is subject to a man-in-the-middle attacker | ||
| − | ** HSTS automatically | + | ** HSTS automatically redirects HTTP requests to HTTPS for the target domain |
* Web application that is intended to be purely HTTPS inadvertently contains HTTP links or serves content over HTTP | * Web application that is intended to be purely HTTPS inadvertently contains HTTP links or serves content over HTTP | ||
| − | ** HSTS automatically | + | ** HSTS automatically redirects HTTP requests to HTTPS for the target domain |
* A man-in-the-middle attacker attempts to intercept traffic from a victim user using an invalid certificate and hopes the user will accept the bad certificate | * A man-in-the-middle attacker attempts to intercept traffic from a victim user using an invalid certificate and hopes the user will accept the bad certificate | ||
** HSTS does not allow a user to override the invalid certificate message | ** HSTS does not allow a user to override the invalid certificate message | ||
Revision as of 13:55, 10 July 2014
Description
HTTP Strict Transport Security (HSTS) is an opt-in security enhancement that is specified by a web application through the use of a special response header. Once a supported browser receives this header that browser will prevent any communications from being sent over HTTP to the specified domain and will instead send all communications over HTTPS. It also prevents HTTPS click through prompts on browsers.
The specification has been released and published end of 2012 as RFC 6797 (HTTP Strict Transport Security (HSTS)) by the IETF. (Reference see in the links at the bottom.)
Examples
Example of the HTTP strict transport security header
Strict-Transport-Security: max-age=31536000
If all subdomains are HTTPS too then the following header is applicable:
Strict-Transport-Security: max-age=31536000; includeSubDomains
Excessively Strict STS
Use caution when setting excessively strict STS policies. Including subdomains should only be used in environments where all sites within your organization for the given domain name require ssl. Max-age limits should be carefully considered as infrequent visitors may find your site inaccessible if you relax your policy.
Browser Support
| Browser |
Support Introduced |
| Internet Explorer |
support expected starting with ie12[1] |
| Firefox |
4 |
| Opera |
12 |
| Safari |
Mavericks (Mac OS X 10.9) |
| Chrome |
4.0.211.0 |
A detailed overview of supporting browsers can be found at canisue.com.
Server Side
The web server side needs to inject the HSTS header.
For HTTP sites on the same domain it is not recommended to add a HSTS header but to do a permanent redirect (301 status code) to the HTTPS site.
An Apache HTTPd example that will permanently redirect a URL to the identical URL with a HTTPS scheme, is as follows:
<VirtualHost *:80>
ServerAlias *
RewriteEngine On
RewriteRule ^(.*)$ https://%{HTTP_HOST}$1 [redirect=301]
</VirtualHost>
On the HTTPS site configuration the following is needed to add the header as recommended by the standard:
Header set Strict-Transport-Security "max-age=31536000; includeSubDomains"
The following links show how to set response headers in other web servers:
IIS
Whilst custom headers can be configured in IIS without any extensions, it is not possible to restrict these headers to secure transport channels as per the HSTS specification. HSTS has been implemented as per the specification as an open source IIS module.
Threats
HSTS addresses the following threats:
- User bookmarks or manually types http://example.com and is subject to a man-in-the-middle attacker
- HSTS automatically redirects HTTP requests to HTTPS for the target domain
- Web application that is intended to be purely HTTPS inadvertently contains HTTP links or serves content over HTTP
- HSTS automatically redirects HTTP requests to HTTPS for the target domain
- A man-in-the-middle attacker attempts to intercept traffic from a victim user using an invalid certificate and hopes the user will accept the bad certificate
- HSTS does not allow a user to override the invalid certificate message
Links
OWASP TLS Protection Cheat Sheet
Moxie Marlinspike's Black Hat 2009 talk on sslstrip, that demonstrates why you need HSTS
