HTTP referer
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In HTTP, " " (originally a misspelling of "Referrer" which has become a common spelling) is an optional HTTP header field that identifies the address of the web page (i.e., the URI or IRI) from which the resource has been requested. By checking the referrer, the server providing the new web page can see where the request originated. In the most common situation, this means that when a user clicks a hyperlink in a web browser, causing the browser to send a request to the server holding the destination web page, the request may include the field, which indicates the last page the user was on (the one where they clicked the link). Web sites and web servers log the content of the received field to identify the web page from which the user followed a link, for promotional or statistical purposes. This entails a loss of privacy for the user and may introduce a security risk. To mitigate security risks, browsers have been steadily reducing the amount of information sent in Referer. As of March 2021, by default Chrome, Chromium-based Edge, Firefox, Safari default to sending only the origin in cross-origin requests, stripping out everything but the domain name.
In HTTP, " " (originally a misspelling of "Referrer" which has become a common spelling) is an optional HTTP header field that identifies the address of the web page (i.e., the URI or IRI) from which the resource has been requested. By checking the referrer, the server providing the new web page can see where the request originated. In the most common situation, this means that when a user clicks a hyperlink in a web browser, causing the browser to send a request to the server holding the destination web page, the request may include the field, which indicates the last page the user was on (the one where they clicked the link). Web sites and web servers log the content of the received field to identify the web page from which the user followed a link, for promotional or statistical purposes. This entails a loss of privacy for the user and may introduce a security risk. To mitigate security risks, browsers have been steadily reducing the amount of information sent in Referer. As of March 2021, by default Chrome, Chromium-based Edge, Firefox, Safari default to sending only the origin in cross-origin requests, stripping out everything but the domain name. == Referrer hiding == Most web servers maintain logs of all traffic, and record the HTTP referrer sent by the web browser for each request. This raises a number of privacy concerns, and as a result, a number of systems to prevent web servers being sent the real referring URL have been developed. These systems work either by blanking the referrer field or by replacing it with inaccurate data. Generally, Internet-security suites blank the referrer data, while web-based servers replace it with a false URL, usually their own. This raises the problem of referrer spam. The technical details of both methods are fairly consistent – software applications act as a proxy server and manipulate the HTTP request, while web-based methods load websites within frames, causing the web browser to send a referrer URL of their website address. Some web browsers give their users the option to turn off referrer fields in the request header. Most web browsers do not send the referrer field when they are instructed to redirect using the "Refresh" field. This does not include some versions of Opera and many mobile web browsers. However, this method of redirection is discouraged by the World Wide Web Consortium (W3C). If a website is accessed from a HTTP Secure (HTTPS) connection and a link points to anywhere except another secure location, then the referrer field is not sent. The HTML5 standard added support for the attribute/value rel="noreferrer" , which instructs the user agent to not send a referrer. Another referrer hiding method is to convert the original link URL to a Data URI scheme-based URL containing small HTML page with a meta refresh to the original URL. When the user is redirected from the data: page, the original referrer is hidden. Content Security Policy standard version 1.1 introduced a new referrer directive that allows more control over the browser's behaviour in regards to the referrer header. Specifically it allows the webmaster to instruct the browser not to block referrer at all, reveal it only when moving with the same origin etc. ==External links== : Hypertext Transfer Protocol -- HTTP/1.0 : Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content : Internationalized Resource Identifiers (IRIs) [//w3c.github.io/webappsec/specs/referrer-policy/ Referrer Policy - W3C Editor's Draft]
Text derived from https://en.wikipedia.org/w/index.php?oldid=1376338446 under CC BY-SA 4.0; modifications have been made.