31/12/12 10:51:33 (10 years ago)

update the description of Referer to current practice and actual security concerns

1 edited


  • draft-ietf-httpbis/latest/p2-semantics.xml

    r2071 r2072  
    269269   When a client constructs an HTTP/1.1 request message, it sends the
    270    "target URI" in one of various forms, as defined in
     270   <x:ref>target URI</x:ref> in one of various forms, as defined in
    271271   (&request-target;). When a request is received, the server reconstructs
    272    an "effective request URI" for the target resource
     272   an <x:ref>effective request URI</x:ref> for the target resource
    273273   (&effective-request-uri;).
    20242024   The asterisk "*" character is used to group media types into ranges,
    20252025   with "*/*" indicating all media types and "type/*" indicating all
    2026    subtypes of that type. The media-range &MAY; include media type
     2026   subtypes of that type. The media-range can include media type
    20272027   parameters that are applicable to that range.
    2030    Each media-range &MAY; be followed by one or more accept-params,
    2031    beginning with the "q" parameter for indicating a relative weight,
    2032    as defined in &qvalue;.
    2033    The first "q" parameter (if any) separates the media-range
    2034    parameter(s) from the accept-params.
     2030   Each media-range might be followed by zero or more applicable media type
     2031   parameters (e.g., <x:ref>charset</x:ref>), an optional "q" parameter for
     2032   indicating a relative weight (&qvalue;), and then zero or more extension
     2033   parameters. The "q" parameter is necessary if any accept-ext are present,
     2034   since it acts as a separator between the two parameter sets.
    23742374  <x:anchor-alias value="Referer"/>
    2376    The "Referer" [sic] header field allows the client to specify the
    2377    URI of the resource from which the target URI was obtained (the
    2378    "referrer", although the header field is misspelled.).
    2379 </t>
    2380 <t>
    2381    The Referer header field allows servers to generate lists of back-links to
    2382    resources for interest, logging, optimized caching, etc. It also allows
    2383    obsolete or mistyped links to be traced for maintenance. Some servers use
    2384    Referer as a means of controlling where they allow links from (so-called
    2385    "deep linking"), but legitimate requests do not always
    2386    contain a Referer header field.
    2387 </t>
    2388 <t>
    2389    If the target URI was obtained from a source that does not have its own
    2390    URI (e.g., input from the user keyboard), the Referer field &MUST; either be
    2391    sent with the value "about:blank", or not be sent at all. Note that this
    2392    requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
     2376   The "Referer" [sic] header field allows the user agent to specify a URI
     2377   reference for the resource from which the <x:ref>target URI</x:ref> was
     2378   obtained (i.e., the "referrer", though the field name is misspelled).
     2379   A user agent &MUST; exclude any fragment or userinfo components
     2380   <xref target="RFC3986"/> when generating the Referer field value.
    23942382<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
     2386   Referer allows servers to generate back-links to other resources for
     2387   simple analytics, logging, optimized caching, etc. It also allows
     2388   obsolete or mistyped links to be found for maintenance. Some servers use
     2389   Referer as a means of denying links from other sites (so-called
     2390   "deep linking") or restricting cross-site request forgery (CSRF),
     2391   but not all requests contain a Referer header field.
    23982394   Example:
    2404    If the field value is a relative URI, it &SHOULD; be interpreted
    2405    relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
    2406    <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
     2400   If the target URI was obtained from a source that does not have its own
     2401   URI (e.g., input from the user keyboard, or an entry within the user's
     2402   bookmarks/favorites), the user agent &MUST; either exclude Referer or
     2403   send it with a value of "about:blank".
     2406   The Referer field has the potential to reveal information about the request
     2407   context or browsing history of the user, which is a privacy concern if the
     2408   referring resource's identifier reveals personal information (such as an
     2409   account name) or a resource that is supposed to be confidential (such as
     2410   behind a firewall or internal to a secured service). Most general-purpose
     2411   user agents do not send the Referer header field when the referring
     2412   resource is a local "file" or "data" URI. A user agent &SHOULD-NOT; send a
     2413   <x:ref>Referer</x:ref> header field in a (non-secure) HTTP request if the
     2414   referring page was received with a secure protocol.
     2415   See <xref target="encoding.sensitive.information.in.uris"/> for additional
     2416   security considerations.
     2419   Some intermediaries have been known to indiscriminately remove Referer
     2420   header fields from outgoing requests. This has the unfortunate side-effect
     2421   of interfering with protection against CSRF attacks, which can be far
     2422   more harmful to their users. Intermediaries and user agent extensions that
     2423   wish to limit information disclosure in Referer ought to restrict their
     2424   changes to specific edits, such as replacing internal domain names with
     2425   pseudonyms or truncating the query and/or path components.
     2426   Intermediaries &SHOULD-NOT; modify or delete the Referer field when the
     2427   field value shares the same scheme and host as the request target.
    47604781<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
    4762    Because the source of a link might be private information or might
    4763    reveal an otherwise private information source, it is strongly
    4764    recommended that the user be able to select whether or not the
    4765    <x:ref>Referer</x:ref> field is sent. For example, a browser client could
    4766    have a toggle switch for browsing openly/anonymously, which would
    4767    respectively enable/disable the sending of Referer and From
    4768    information.
    4769 </t>
    4770 <t>
    4771    Clients &SHOULD-NOT; include a <x:ref>Referer</x:ref> header field in a
    4772    (non-secure) HTTP request if the referring page was transferred with a secure
    4773    protocol.
     4783   URIs are intended to be shared, not secured, even when they identify secure
     4784   resources.  URIs are often shown on displays, added to templates when a page
     4785   is printed, and stored in a variety of unprotected bookmark lists.
     4786   It is therefore unwise to include information within a URI that
     4787   is sensitive, personally identifiable, or a risk to disclose.
     4790   Since the Referer header field tells a target site about the context that
     4791   resulted in a request, it has the potential to reveal information about the
     4792   user's immediate browsing history and any personal information that might
     4793   be found in the referring resource's URI. Further discussion of Referer
     4794   considerations can be found in <xref target="header.referer"/>.
    47774798   sensitive data because that data will be placed in the request-target. Many
    47784799   existing servers, proxies, and user agents log or display the request-target
    4779    in places where it might be visible to third parties. Such services can
    4780    use POST-based form submission instead.
     4800   in places where it might be visible to third parties. Such services ought
     4801   to use POST-based form submission instead.
    48814902    <x:defines>Upgrade</x:defines>
    48824903    <x:defines>Via</x:defines>
     4904    <x:defines>effective request URI</x:defines>
     4905    <x:defines>target URI</x:defines>
    48834906  </x:source>
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