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HTTP referer
HTTP referer
HTTP referer
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In HTTP, "Referer" (a misspelling of "Referrer"[1]) 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 Referer 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 Referer field to identify the web page from which the user followed a link, for promotional or statistical purposes.[citation needed] This entails a loss of privacy for the user and may introduce a security risk.[2] To mitigate security risks, browsers have been steadily reducing the amount of information sent in Referer. As of March 2021, by default Chrome,[3] Chromium-based Edge, Firefox,[4] Safari[5] default to sending only the origin in cross-origin requests, stripping out everything but the domain name.

Etymology

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The misspelling of referrer was introduced in the original proposal by computer scientist Phillip Hallam-Baker to incorporate the "Referer" header field into the HTTP specification.[6][7] The misspelling was set in stone by the time (May 1996) of its incorporation into the Request for Comments standards document RFC 1945[8] (which 'reflects common usage of the protocol referred to as "HTTP/1.0"' at that time); document co-author Roy Fielding remarked in March 1995 that "neither one (referer or referrer) is understood by" the standard Unix spell checker of the period.[9] "Referer" has since become a widely used spelling in the industry when discussing HTTP referrers; usage of the misspelling is not universal, though, as the correct spelling "referrer" is used in some web specifications such as the Referrer-Policy HTTP header or the Document Object Model.[2]

Details

[edit]

When visiting a web page, the referrer or referring page is the URL of the previous web page from which a link was followed.

More generally, a referrer is the URL of a previous item which led to this request. For example, the referrer for an image is generally the HTML page on which it is to be displayed. The referrer field is an optional part of the HTTP request sent by the web browser to the web server.[10]

Many websites log referrers as part of their attempt to track their users. Most web log analysis software can process this information. Because referrer information can violate privacy, some web browsers allow the user to disable the sending of referrer information.[11] Some proxy and firewall software will also filter out referrer information, to avoid leaking the location of non-public websites. This can, in turn, cause problems: some web servers block parts of their website to web browsers that do not send the right referrer information, in an attempt to prevent deep linking or unauthorised use of images (bandwidth theft). Some proxy software has the ability to give the top-level address of the target website as the referrer, which reduces these problems but can still in some cases divulge the user's last-visited web page.

Many blogs publish referrer information in order to link back to people who are linking to them, and hence broaden the conversation. This has led, in turn, to the rise of referrer spam: the sending of fake referrer information in order to popularize the spammer's website.

It is possible to access the referrer information on the client side using document.referrer in JavaScript.[12] This can be used, for example, to individualize a web page based on a user's search engine query. However, the referrer field does not always include search keywords, such as when using Google Search with HTTPS.[13]

Referrer hiding

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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.[11]

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).[14]

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.[10]

The HTML5 standard added support for the attribute/value rel="noreferrer", which instructs the user agent to not send a referrer.[15]

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.[16]

References

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HTTP referer

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The HTTP Referer header (often misspelled as "referer" in the specification rather than the correct English spelling "referrer") is an optional HTTP request header field that identifies the URI of the resource from which the (such as a ) initiated the request, allowing the receiving server to determine the referring page or context. This header was first defined in HTTP/1.0 and formalized in subsequent standards, enabling servers to track navigation origins for purposes like , , of back-link lists, and basic checks against unauthorized access. The value is typically a full URI or a relative reference to the previous resource, but its inclusion is not mandatory and depends on configuration, protocol security levels, and policy settings. While useful for legitimate web operations, the Referer header raises significant and concerns because it can inadvertently disclose sensitive , such as query parameters containing , tokens, or full URLs from secure () contexts when requests are made to insecure (HTTP) endpoints. For instance, clicking a link from a banking site to an external resource might expose the full referral URL, including account details, to third-party servers, potentially enabling tracking or attacks. To mitigate these risks, modern web standards introduce the Referrer-Policy response header, which allows site owners to control the amount of referrer sent—options include stripping the path, origin only, or no referrer at all—and user agents often default to stricter policies for cross-origin requests or when upgrading from HTTP to . Additionally, browsers may omit the header entirely in private browsing modes or when navigating from secure to insecure sites to protect user . The header's syntax follows the ABNF notation as Referer = absolute-URI / partial-URI, where it is sent only in requests (not responses) and is case-insensitive, though implementations typically use "Referer". Despite its utility in and anti-bot measures, evolving regulations like GDPR and browser features such as Intelligent Tracking Prevention have led to reduced reliance on Referer , with alternatives like the Fetch Metadata Request Headers providing safer context without full exposure. Overall, while the Referer remains a core part of HTTP semantics, its use is increasingly balanced against user protections in contemporary .

Origins and Etymology

Etymology

The HTTP "Referer" header derives its name from a misspelling of the standard English term "referrer," which denotes the source providing a reference or directing a user to another resource. This typographical error occurred in the initial proposal for the header by computer scientist Phillip Hallam-Baker, who suggested incorporating the field into the HTTP specification. Hallam-Baker later acknowledged responsibility for the error in a 1995 IETF mailing list discussion, noting that he had suggested the field without initially naming it, and Roy Fielding proposed the misspelled "Referer" as the header name. The misspelling persisted into the formal HTTP/1.0 specification published as RFC 1945 in 1996, where it was defined without correction due to emerging implementations already adopting the term. Subsequent standards, including HTTP/1.1 in RFC 2616 (1999) and later revisions, retained "Referer" to ensure with existing web infrastructure, avoiding disruptions to deployed systems. Early contributors from the IETF working group, including , prioritized protocol stability over orthographic accuracy, solidifying the non-standard spelling across the web ecosystem. Linguistically, "referer" functions as a from "referral," treating the header as an agent of the referral process, but it deviates from conventional English morphology where "referrer" preserves the double 'r' from the verb "refer" (as in "" from "program"). This irregularity mirrors other technical terms where variant spellings have become entrenched, such as "" () versus "" (), both accepted despite differing conventions. The persistence of "referer" underscores how protocol design often favors practical consistency over linguistic precision in standards.

Historical Development

The HTTP referer header was first introduced as an optional request header in the HTTP/1.0 specification, although it first appeared in early HTTP drafts, including the W3C request headers specification updated on May 3, 1994, outlined in RFC 1945 and published in May 1996. Defined in Section 10.13, it specified the URI of the originating resource—typically from a or form submission—to assist servers in generating back-links, logging navigation patterns, optimizing caching, and tracing issues like obsolete links. The header's syntax allowed for absolute or relative URIs, though fragments were excluded, and it was not required for requests lacking a clear origin, such as direct keyboard input. Authors , Roy T. Fielding, and Henrik Frystyk Nielsen emphasized user control over its transmission due to early considerations. The header persisted without alteration in the HTTP/1.1 specification, formalized in RFC 2616 and published in June 1999, maintaining its role in enabling server-side analysis while recommending against its use in non-secure requests following secure ones to protect sensitive URIs. During the mid-1990s, initial browser support emerged with implementations in early web clients like (version 1.0 released in December 1994) and successors, aligning with the growing adoption of HTTP for hypermedia systems. In the late 1990s, the referer became instrumental in rudimentary , as server log analyzers such as Analog (launched in 1995) parsed it to track referral sources and user paths on nascent websites. By the early 2000s, growing recognition of risks—such as unintended disclosure of browsing history or secure site details—prompted partial browser implementations, including options to suppress or strip the header in cross-protocol transitions (e.g., to HTTP). This evolution culminated in the 2014 update via RFC 7231, which redefined HTTP/1.1 semantics across multiple documents but retained the referer header's name and function unchanged for , despite ongoing discussions within the IETF HTTP Working Group about potential renaming to "referrer" that were ultimately rejected to avoid breaking existing systems. The specification reiterated safeguards, advising against its inclusion in downgraded security contexts.

Technical Functionality

Header Syntax and Values

The Referer header field follows the general HTTP header syntax, consisting of the field name "Referer" followed by a colon and a space, then the field value as a URI reference that identifies the referring resource from which the request originated. The value adheres to the URI-reference production defined in RFC 3986, allowing either an absolute URI or a partial URI (relative reference). This structure enables servers to contextualize requests without requiring a full in all cases. Possible values for the Referer header include absolute URLs, such as https://example.com/page.html, which specify the complete scheme, host, path, and optional query parameters. Partial URIs, like /path/to/resource?query=value, represent relative paths from the same origin, omitting the scheme and components. An empty value or omission of the header indicates no referrer information is provided, often due to policy or lack of a referring context. Encoding rules for the Referer value require percent-encoding of special characters as per URI syntax in RFC 3986; for instance, spaces are encoded as %20, and non-ASCII characters use UTF-8 percent-encoding. Query parameters are included if present in the referring URI, but the fragment identifier (e.g., #section) must not be sent, as it is client-side and irrelevant to the server. This ensures the value remains a valid, parsable reference without extraneous components. In edge cases involving origins requesting mixed content over HTTP, user agents SHOULD NOT send the Referer header to prevent leakage of secure URL details. For invalid or malformed values, such as non-URI strings, HTTP servers handle them as opaque strings per general field parsing rules, often ignoring or logging them without error. The formal grammar for the Referer header, as specified in RFC 9110 (which obsoletes RFC 7231), is given in Augmented Backus-Naur Form (ABNF) below:

Referer = absolute-URI / partial-URI absolute-URI = scheme ":" hier-part [ "?" query ] partial-URI = relative-part [ "?" query ]

Referer = absolute-URI / partial-URI absolute-URI = scheme ":" hier-part [ "?" query ] partial-URI = relative-part [ "?" query ]

These productions reference additional definitions from RFC 9110 (e.g., query, hier-part, relative-part) and RFC 3986 for complete URI components.

Usage in HTTP Requests and Responses

The HTTP Referer header is exclusively a request header field sent by s, such as web browsers, to indicate the address of the referring from which the current request originated. It is included in outgoing HTTP requests when the fetches a that was invoked or obtained from another URI, enabling the recipient server to identify the source for purposes like logging or link validation. According to the HTTP/1.1 specification, s SHOULD send the Referer field whenever they have knowledge of the referring URI, but its inclusion is optional and subject to choices. User agents trigger the Referer header in various resource fetch scenarios, including navigation via hyperlinks (e.g., clicking an tag to perform a GET request), form submissions (e.g., POST requests from
elements), and loading embedded resources such as images via tags, scripts via In practice, the Referer appears in the request headers of both GET and POST methods. For example, a GET request triggered by clicking a link from https://example.com/page1 to https://target.com/page2 might include:

GET /page2 HTTP/1.1 Host: target.com Referer: https://example.com/page1

GET /page2 HTTP/1.1 Host: target.com Referer: https://example.com/page1

Similarly, a POST request from a form submission on the same referring page would carry the identical Referer value, allowing the server to associate the action with its origin. The header value is typically the full URI of the referring page, though it may be truncated to the origin in certain cross-origin scenarios depending on browser policies. Although the Referer header is defined solely for requests and is rarely, if ever, used in HTTP responses per the standards, servers receiving it perform various processing tasks. Servers parse the Referer to log traffic sources for , enabling site owners to track referral patterns and optimize content placement. It also supports security measures, such as anti-forgery checks in (CSRF) prevention, where the server verifies that the request originates from an expected domain to block unauthorized actions. Furthermore, servers may use the Referer for conditional redirects, such as tailoring destination URLs based on the incoming source to enhance or enforce access controls.

Privacy and Security Aspects

Privacy Risks and Concerns

The HTTP Referer header poses significant risks by automatically disclosing the full of the originating page to third-party servers when users navigate via links, forms, or embedded resources, potentially exposing sensitive query parameters such as search terms, session IDs, or personal identifiers. For instance, a containing a search query like https://example.com/search?q=confidential+medical+condition can reveal private user interests or health details to unrelated domains, including advertisers or providers, without user consent. Similarly, session tokens or tracking IDs embedded in may be leaked, enabling unauthorized reconstruction of user sessions across sites. This leakage facilitates cross-site tracking, where third-party services, such as firms, use Referer data to correlate user browsing paths and build detailed profiles spanning multiple domains. By receiving the originating , trackers can infer sequences of visited pages, interests, and behaviors, even if the user has not directly interacted with their domain, thereby undermining efforts to compartmentalize online activities. This mechanism has been a foundational enabler of pervasive in web ecosystems, allowing entities like to link cross-domain activities for . Historically, in the early 2000s, default browser behaviors sent full Referer headers without restrictions, leading to widespread unintended disclosures; for example, Google appended users' search queries to Referer headers in HTTP requests, violating privacy expectations and prompting later legal scrutiny over data practices from that era. Notable incidents included the leakage of password reset tokens via Referer when users clicked external links from secure pages, as documented in vulnerability reports where such tokens enabled unauthorized account access if intercepted by third parties. These early defaults amplified risks, as web applications often included sensitive parameters in URLs without anticipating their transmission to external sites. In the modern context as of 2025, risks have intensified with the proliferation of personalized URLs in , where dynamic links embed user-specific data like cart contents or affiliate trackers, increasing the potential for leakage to payment processors or ad networks during cross-origin navigations. Browser behaviors continue to default to sending Referers unless explicitly configured otherwise, exacerbating exposures in scenarios involving embedded buttons or analytics scripts on sensitive pages. Quantitative studies underscore the scale of these issues; for example, analysis of over 3,000 websites in 2022 revealed that more than 90% circumvented strict Referer policies, resulting in the leakage of visited URLs to third parties, predominantly . Additionally, research from 2022 found that approximately 80% of top websites with search functionality leaked user search terms to advertisers via Referer headers, highlighting the ongoing prevalence of such tracking despite privacy enhancements. These findings indicate that Referer-based exposures remain a dominant vector for erosion in contemporary .

Security Implications

The HTTP Referer header plays a role in mitigating Cross-Site Request Forgery (CSRF) attacks by allowing servers to verify that sensitive requests originate from trusted pages within the expected domain. In CSRF prevention, applications can check the Referer to ensure it matches an allowed origin, thereby blocking forged requests from external sites that lack the user's session credentials. This approach was particularly common in early web applications before widespread adoption of synchronizer tokens. However, reliance on the Referer for introduces significant risks due to its manipulability. Attackers can spoof the Referer header in non-browser clients, such as using tools like with the --referer option to arbitrarily set the value, bypassing domain checks in automated or scripted attacks. Additionally, open redirect vulnerabilities enable malicious sites to forge trusted Referers; for instance, an attacker might lure users to an open redirect endpoint on a legitimate domain that then forwards to the attacker's page, making subsequent requests appear to originate from the trusted source. These techniques undermine Referer-based defenses, allowing unauthorized actions like unauthorized fund transfers or account changes. In May 2025, a vulnerability in (CVE-2025-4664) was disclosed, allowing attackers to leak cross-origin data by exploiting the Referrer Policy via the Link header in crafted pages, enabling capture of full URLs including sensitive query parameters. This flaw, with a CVSS score of 4.3, was actively exploited in the wild and patched in Chrome version 136.0.7103.113 and later. To address these threats, security best practices recommend treating the Referer as a supplemental control rather than a primary mechanism, always combining it with stronger measures like CSRF tokens. Servers should implement strict validation by whitelisting specific domains or paths in the Referer value, rejecting any mismatches or absences, as outlined in guidelines. For example, parsing the Referer to extract and verify only the origin against a predefined allowlist prevents partial matches or manipulations that could spoof trusted origins. Historically, pre-2010 web applications frequently exploited flawed Referer checks in CSRF scenarios, contributing to vulnerabilities listed in the OWASP Top 10 for 2010, where inadequate origin validation enabled widespread attacks on session-based systems. Such exploits highlighted the header's unreliability, prompting shifts toward more robust defenses in subsequent years.

Modern Policies and Implementations

Referrer-Policy Header

The Referrer-Policy response header enables web servers to specify how much referrer information is included in the Referer header of outgoing requests made by clients, thereby controlling the disclosure of the originating URL. This mechanism addresses privacy concerns by allowing fine-grained control over referrer transmission during navigations, resource fetches, and prefetches. Standardized in the W3C Referrer Policy specification on 26 January 2017, it was integrated into the WHATWG Fetch living standard to provide a consistent policy framework across web platforms. The syntax of the header is straightforward: Referrer-Policy: <policy-token>[, <policy-token>]*, where each policy-token is one of several predefined values that dictate referrer behavior. Multiple tokens can be specified, with the first applicable one used for a given request; if none match, the request falls back to the client-default policy. The available policy tokens include:
  • no-referrer: The Referer header is omitted entirely from all requests, providing maximum by sending no origin information.
  • no-referrer-when-downgrade: The full referrer URL is sent for requests using the same or a secure protocol (e.g., to ), but stripped entirely when downgrading from to HTTP to prevent leakage to insecure contexts.
  • origin: Only the origin (scheme, host, and port) of the referrer is sent, omitting the path and query parameters for reduced exposure.
  • origin-when-cross-origin: The full referrer URL is sent for same-origin requests, but only the origin for cross-origin requests, regardless of protocol downgrade.
  • same-origin: The full referrer URL is sent only for same-origin requests; cross-origin requests omit the Referer header.
  • strict-origin: Similar to the "origin" policy, but the Referer header is stripped entirely for cross-origin requests that would downgrade from to HTTP.
  • strict-origin-when-cross-origin: The full referrer is sent for same-origin requests, the origin only for cross-origin same-scheme requests, and nothing for cross-origin downgrades.
  • unsafe-url: The full referrer URL, including path and query, is sent regardless of origin or protocol, which can expose sensitive data and is generally discouraged.
These policies influence the referrer algorithm in the Fetch standard, determining whether and what portion of the referrer is populated based on the request's context, such as navigation type or resource fetch. For instance, under no-referrer-when-downgrade, an HTTPS-to-HTTP navigation would result in no Referer header, while an HTTPS-to-HTTPS fetch would include the full URL. The specification's default policy is strict-origin-when-cross-origin. In the absence of an explicit Referrer-Policy header, browsers apply default policies to ensure baseline privacy protections. For example, Google Chrome has used strict-origin-when-cross-origin as its default since version 85 in July 2020, prioritizing origin-only disclosure for cross-origin requests while stripping on downgrades. Other browsers, such as Firefox and Safari, similarly default to strict-origin-when-cross-origin or equivalent behaviors to align with evolving privacy standards. Recent enhancements to the specification, reflected in updates to the WHATWG Fetch standard through 2023, have emphasized stricter default policies and better integration with privacy regulations like the EU's GDPR (effective 2018) and California's CCPA (effective 2020), promoting reduced referrer leakage to mitigate tracking risks without breaking web functionality. These updates include refined policy resolution for nested browsing contexts and improved handling of service workers, ensuring consistent application across modern web ecosystems.

Browser and Server-Side Controls

Browsers implement varying default referrer policies to balance privacy and functionality, with differences arising from historical and security priorities. has adopted strict-origin-when-cross-origin as its default policy since version 85 in 2020, stripping path and query parameters for cross-origin requests while sending the origin for same-origin ones, enhancing user privacy without breaking most web applications. Mozilla Firefox historically defaulted to unsafe-url, which sent the full referrer including path and query strings, but shifted to strict-origin-when-cross-origin starting with version 87 in March 2021 to mitigate tracking risks, though legacy configurations may still enforce the older behavior in certain preferences. Apple Safari enforces strict-origin-when-cross-origin as its default since Safari 14 in 2020, limiting referrers to the origin only for cross-origin HTTPS-to-HTTP downgrades and omitting them entirely in such cases, aligning with stricter privacy controls in . Server-side configurations allow administrators to enforce referrer policies globally or per-resource via HTTP headers, overriding or complementing browser defaults. In , the mod_headers module enables setting the policy using directives like Header always set Referrer-Policy "strict-origin-when-cross-origin" within a <VirtualHost> or .htaccess file, applying to all responses and ensuring consistent behavior across clients. Similarly, supports this through the add_header directive, such as add_header Referrer-Policy strict-origin-when-cross-origin always; in the server block of the configuration file, which propagates the policy to browsers during resource delivery and supports conditional logic via if statements for specific paths. documents can also impose client-side controls using the <meta name="referrer" content="strict-origin-when-cross-origin"> tag in the <head> section, which browsers like Chrome and honor to set the policy for all outgoing requests from that page, providing a fallback when server headers are unavailable. Client-side further refines referrer control through APIs like the Fetch interface, where developers specify a referrerPolicy option—such as 'strict-origin-when-cross-origin'—in fetch() calls to dictate referrer inclusion for programmatic requests, overriding document-level settings as of implementations in major browsers. This allows dynamic adjustment, for instance, in single-page applications where fetch([url](/page/URL), { referrerPolicy: 'no-referrer' }) suppresses the referrer entirely for sensitive calls, though it requires explicit handling to avoid leaking information via default behaviors. Referrer handling remains compliant with and standards, as these protocols preserve semantic headers like Referer without alteration, though 's transport may introduce minor latency differences in header transmission due to multiplexing. Edge cases between mobile and desktop browsers often stem from platform-specific features; for example, mobile via applies more aggressive referrer stripping in cross-site contexts compared to desktop macOS versions, potentially omitting referrers in embedded iframes to prevent tracking in touch-optimized environments. Recent updates in 2024 have intensified privacy measures, particularly Apple's Intelligent Tracking Prevention (ITP), which blocks or strips referrer information for cross-site navigations in 18 and later, extending to third-party embeds. These changes, effective across 18 and macOS Sequoia, align with broader ecosystem shifts toward zero-knowledge referrer transmission in privacy-focused modes.

Hiding and Manipulation Techniques

Methods to Suppress or Alter Referrer

Client-side techniques allow web developers to suppress or alter the Referer header directly within or . One common method is using the <meta name="referrer"> tag in the document's <head> section, which sets a referrer policy for all requests originating from that page. For instance, <meta name="referrer" content="no-referrer"> instructs the browser to omit the Referer header entirely for subsequent navigations, resource loads, and subresource requests. In , the Fetch API provides the referrerPolicy option to control referrer transmission on a per-request basis. Developers can specify policies like 'no-referrer' when initiating a fetch, ensuring no Referer header is sent with the request, regardless of the document's global policy. This is particularly useful for AJAX calls or dynamic resource loading where fine-grained control is needed. Browser extensions offer user-configurable ways to strip or block referrers across sessions, enhancing privacy without altering site code. Tools like , released in 2015, can modify referrer policies or block transmission to third-party domains through custom filters and settings, preventing leakage in cross-site requests. Similarly, , launched in 2015 by the , blocks referrer information for heuristically identified trackers on yellowlisted domains while allowing essential functionality. These extensions gained widespread adoption in the amid rising privacy concerns. Server-side approaches involve intermediaries that rewrite or remove the Referer header before forwarding requests. Reverse proxies, such as those configured with , can use directives like proxy_set_header Referer ""; to blank the header or replace it with a sanitized value, anonymizing the origin for backend services. URL rewriting modules, like 's rewrite or Apache's mod_rewrite, enable pattern-based modifications to strip sensitive path or query components from the Referer while preserving the domain, thus reducing information disclosure. These methods are effective for anonymizing traffic in proxy chains but require careful configuration to avoid breaking referrer-dependent features. Protocol-level tricks provide additional ways to minimize referrer exposure in specific contexts. Using HTTP POST requests instead of GET can avoid embedding sensitive data in URLs that might otherwise be exposed via the Referer header during subsequent navigations, though the header itself is still sent if the request originates from a referring page. Data URLs (data: scheme) and blob URLs (blob: scheme) bypass traditional referrer transmission by embedding content directly in the page or creating temporary in-memory objects, preventing network requests that would include a Referer; for example, loading an image via <img src="data:image/..."> generates no external fetch. These are useful for small, self-contained resources but are limited to inline data. Despite these methods, suppressing the Referer header is not universally effective as of 2025, particularly for passive resource loads like images embedded via <img> tags, where browser defaults or incomplete policy inheritance may still transmit partial referrer data in legacy or non-compliant scenarios. Techniques reliant on client-side controls can be overridden by user agents or fail against service worker-intercepted requests, and server-side proxies do not influence direct client-to-server communications outside their scope. Comprehensive suppression often requires combining multiple approaches with the Referrer-Policy header for broader coverage.

Common Use Cases for Hiding

One primary for hiding the HTTP Referer header is privacy protection, where users and websites seek to prevent unauthorized tracking across domains, particularly in advertising ecosystems and interactions. The Referer header can disclose the originating , including query parameters that reveal user behavior or sensitive navigation paths, enabling third-party trackers to build detailed profiles . For instance, when users share links on social platforms, the Referer may expose the source page to external sites, facilitating cross-site correlation of activities. To mitigate this, browsers and sites employ policies like "no-referrer" to suppress the header entirely, reducing the risk of such leakage and enhancing user in online browsing. Enterprises often hide the Referer to safeguard internal URLs and information when linking to external resources, thereby preventing competitors from gaining on site structure or user flows. Sensitive data embedded in URLs, such as session tokens or internal paths, could be inadvertently shared via the Referer during cross-origin requests, potentially exposing operations or confidential patterns. By implementing strict Referrer-Policy settings, organizations ensure that outbound links do not transmit these details, maintaining competitive advantages in digital environments. Compliance with data protection regulations like the EU's (GDPR, effective 2018) and California's Consumer Privacy Act (CCPA, effective 2020) drives the suppression of the Referer header to minimize unnecessary sharing. Under GDPR's data minimization principle (Article 5), controllers must limit to what is essential, and the Referer can qualify as if it includes identifiable elements like user-specific parameters. Similarly, CCPA emphasizes consumer rights to limit data sales, where Referer leakage could contribute to unauthorized profiling. Adopting no-referrer policies helps organizations demonstrate adherence by curbing cross-site data flows, avoiding potential fines up to 4% of global annual turnover under GDPR. In , hiding the Referer prevents leaks in links and sensitive forms, preserving intended traffic attribution and user trust. Affiliate programs rely on precise referral tracking, but exposed Referers from intermediate pages can dilute commissions or reveal promotional strategies to rivals. For sensitive forms, such as or interfaces, suppressing the header avoids transmitting originating URLs that might contain confidential details to third-party scripts or resources. Designers use attributes like rel="noreferrer" on or server-side headers to achieve this, ensuring cleaner without compromising functionality. The have seen a surge in Referer hiding aligned with the shift toward zero-party data preferences, as privacy regulations and browser changes amplify demands for reduced tracking surfaces. Although announced plans to deprecate third-party cookies starting in 2020, these were ultimately abandoned as of 2025, marketers have increasingly favored controlled methods, where Referer suppression complements first-party strategies by limiting passive cross-domain insights. This trend reflects broader adoption of -by-design principles.

References

  1. https://datatracker.ietf.org/doc/html/rfc7231#section-5.5.3
  2. https://developer.mozilla.org/en-US/docs/Web/Security/Referer_header:_privacy_and_security_concerns
  3. https://web.dev/articles/referrer-best-practices
  4. https://lists.w3.org/Archives/Public/ietf-http-wg-old/1995JanApr/0109.html
  5. https://english.stackexchange.com/questions/42630/referer-or-referrer
  6. https://www.w3.org/Protocols/HTTP/HTRQ_Headers.html
  7. https://datatracker.ietf.org/doc/html/rfc1945#section-10.13
  8. https://datatracker.ietf.org/doc/html/rfc2616#section-14.36
  9. https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.36
  10. https://amplitude.com/blog/the-early-days-of-web-analytics
  11. https://ec.europa.eu/justice/article-29/documentation/opinion-recommendation/files/2000/wp37_en.pdf
  12. https://datatracker.ietf.org/doc/html/rfc7231#section-5.5.2
  13. https://datatracker.ietf.org/doc/html/rfc9110
  14. https://datatracker.ietf.org/doc/html/rfc9110#section-15.4
  15. https://datatracker.ietf.org/doc/html/rfc9110#section-10.1.1
  16. https://owasp.org/www-community/attacks/csrf
  17. https://portswigger.net/kb/issues/00500400_cross-domain-referer-leakage
  18. https://petsymposium.org/popets/2025/popets-2025-0092.pdf
  19. https://www.theregister.com/2023/06/17/google_searchers_from_years_past/
  20. https://hackerone.com/reports/751581
  21. https://thoughtbot.com/blog/is-your-site-leaking-password-reset-links
  22. https://www.dataart.team/articles/referer-header-security-risks-and-mitigation-strategies
  23. https://www.cs.ru.nl/masters-theses/2022/T_van_Ouwerkerk___Evading_the_policy:_a_measurement_on_referrer_policy_circumvention_in_3k_e-commerce_websites.pdf
  24. https://www.bleepingcomputer.com/news/security/over-80-percent-of-the-top-websites-leak-user-searches-to-advertisers/
  25. https://www.gendigital.com/blog/archive/search-privacy-research
  26. https://cheatsheetseries.owasp.org/cheatsheets/Cross-Site_Request_Forgery_Prevention_Cheat_Sheet.html
  27. https://cwe.mitre.org/data/definitions/352.html
  28. https://portswigger.net/web-security/csrf/bypassing-referer-based-defenses
  29. https://portswigger.net/web-security/csrf
  30. https://thehackernews.com/2025/05/new-chrome-vulnerability-enables-cross.html
  31. https://owasp.org/www-project-secure-coding-practices-quick-reference-guide/stable-en/02-checklist/05-checklist
  32. https://www.w3.org/TR/referrer-policy/
  33. https://fetch.spec.whatwg.org/#referrer-policy
  34. https://fetch.spec.whatwg.org/
  35. https://www.w3.org/TR/referrer-policy/#referrer-policy-header-syntax
  36. https://www.w3.org/TR/referrer-policy/#no-referrer-when-downgrade-policy
  37. https://www.w3.org/TR/referrer-policy/#same-origin
  38. https://www.w3.org/TR/referrer-policy/#strict-origin-when-cross-origin
  39. https://fetch.spec.whatwg.org/#determine-requests-referrer
  40. https://w3c.github.io/webappsec-referrer-policy/
  41. https://fetch.spec.whatwg.org/#concept-request-referrer-policy
  42. https://blog.mozilla.org/security/2021/03/22/firefox-87-trims-http-referrers-by-default-to-protect-user-privacy/
  43. https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/meta/name/referrer
  44. https://developer.mozilla.org/en-US/docs/Web/API/Request/referrerPolicy
  45. https://datatracker.ietf.org/doc/html/rfc9114
  46. https://developer.mozilla.org/en-US/docs/Web/API/Window/fetch
  47. https://help.sealmetrics.com/en/articles/11125734-understanding-referrer-loss-and-direct-traffic-in-sealmetrics
  48. https://academized.com/blog/eff-privacy-badger
  49. https://github.com/gorhill/uBlock/issues/3604
  50. https://stackoverflow.com/questions/48320831/nginx-how-to-change-request-header-referer
  51. https://serverfault.com/questions/757732/nginx-change-referer-for-proxy
  52. https://security.stackexchange.com/questions/27906/playing-with-referer-header
  53. https://github.com/w3c/webappsec-referrer-policy/issues/95
  54. https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Referrer-Policy
  55. https://www.salesforce.com/blog/dont-let-sensitive-data-hide-in-your-urls/
  56. https://gdpr-info.eu/art-5-gdpr/
  57. https://blog.short.io/how-to-protect-your-referrer-links-with-short-io/
  58. https://iabeurope.eu/wp-content/uploads/2022/03/IAB-Europe-Guide-to-a-Post-Third-Party-Cookie-Era_March-2022.pptx.pdf
  59. https://www.cookieyes.com/blog/cookieless-marketing/
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