WEBSEC
Internet Engineering Task Force (IETF)                           D. Ross
Internet-Draft
Request for Comments: 7034                                     Microsoft
Intended status:
Category: Informational                                       T. Gondrom
Expires: February 28, 2014
ISSN: 2070-1721                                           Thames Stanley
                                                         August 27,
                                                            October 2013

                   HTTP Header Field X-Frame-Options
                  draft-ietf-websec-x-frame-options-12

Abstract

   To improve the protection of web applications against Clickjacking, clickjacking,
   this definition document describes the X-Frame-Options HTTP response header
   field that field, which
   declares a policy policy, communicated from the server to the client browser on
   browser, regarding whether the browser may display the transmitted
   content in frames that are part of other web pages.  This
   informational document serves to document the existing use and
   specification of this X-Frame-Options HTTP response header field.

Status of This Memo

   This Internet-Draft document is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list  It represents the consensus of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a maximum candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of six months this document, any errata,
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   This Internet-Draft will expire on February 28, 2014.
   http://www.rfc-editor.org/info/rfc7034.

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   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . .   2 .  3
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  3
   2.  X-Frame-Options Header . . . . . . . . . . . . . . . . . . .   3 .  4
     2.1.  Syntax . . . . . . . . . . . . . . . . . . . . . . . . .   3 .  4
     2.2.  Augmented Backus-Naur Form (ABNF)  . . . . . . . . . . . .  5
       2.2.1.  Examples of X-Frame-Options  . . . . . . . . . . . . .   5  6
     2.3.  Design Issues  . . . . . . . . . . . . . . . . . . . . . .   5  6
       2.3.1.  Enable HTML content Content from other domains Other Domains . . . . . . . .  6
       2.3.2.  Browser Behaviour Behavior and Processing  . . . . . . . . . . .  6
         2.3.2.1.  Violation of X-Frame-Options . . . . . . . . . . .  6
         2.3.2.2.  Variation in current browser behaviour Current Browser Behavior  . . . . .   6 .  7
         2.3.2.3.  Usage design pattern Design Pattern and example scenario Example Scenario for
                   the ALLOW-FROM parameter  . Parameter . . . . . . . . . . . . .  8
         2.3.2.4.  No caching Caching of the X-Frame-Options header Header . . . . .  8
   3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
     4.1.
     3.1.  Registration Template  . . . . . . . . . . . . . . . . . .  9
   5.
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
     5.1.
     4.1.  Privacy Considerations . . . . . . . . . . . . . . . . . . 10
   6.
   5.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     6.1.
     5.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     6.2.
     5.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Appendix A.  Browsers that support That Support X-Frame-Options . . . . . . .  12 . 13
   Appendix B.  Description of a Clickjacking attack Attack  . . . . . . . .  12 13
     B.1.  Shop . . . . . . . . . . . . . . . . . . . . . . . . . .  12 . 13
     B.2.  Online Shop Confirm Purchase Page  . . . . . . . . . . . .  12 13
     B.3.  Flash Configuration  . . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses  . . . . .
   Appendix C.  Acknowledgements  . . . . . . . . . . . . . . . . . . 13

1.  Introduction

   In 2009 and 2010 2010, many browser vendors ([Microsoft-X-Frame-Options],
   [CLICK-DEFENSE-BLOG], and [Mozilla-X-Frame-Options]) introduced the
   use of a non-standard HTTP [RFC2616] header field "X-Frame-Options"
   to protect against Clickjacking clickjacking [Clickjacking].  HTML-based web
   applications can embed or "frame" other web pages.  Clickjacking is a
   type of attack that occurs when an attacker uses multiple transparent
   or opaque layers in the user interface to trick a user into clicking
   on a button or link on another page from server B when they were
   intending to click on the same place of the overlaying page from
   server A.  Thus, the attacker is "hijacking" clicks meant for their page A
   and routing them to another page B.  The attacker is tricking the user (who
   sees the overlaying user interface content from page A) into clicking
   specific locations on the underlying page from server B, triggering
   some actions on server B and potentially using an existing session
   context in that step.  This is an attack on both the user and on
   server B.  And  In addition, server A may or may not be the attacker.

   This specification provides informational documentation about the
   current use and definition of the X-Frame-Options HTTP header field.
   As described in Section 2.3.2.2 2.3.2.2, not all browsers implement X-Frame-
   Options exactly
   X-Frame-Options in exactly the sames same way, which can lead to unintended
   results.  And  And, given that the "X-" construction is deprecated
   [RFC6648], the X-Frame-Options header field will be replaced in the
   future be
   replaced by the Frame-Options directive in the Content Security Policy Version
   (CSP) version 1.1 [CSP-1-1].

   Existing anti-ClickJacking

   A study [FRAME-BUSTING] demonstrated that existing anti-clickjacking
   measures, e.g.  Frame-breaking Javascript, e.g., frame-breaking JavaScript, have weaknesses so that allow
   their protection can to be circumvented as a
   study [FRAME-BUSTING] demonstrated. circumvented.

   Short of configuring the browser to disable frames and script scripts
   entirely, which massively impairs browser utility, browser users are
   vulnerable to this type of attack.

   The use of "X-Frame-Options" allows a web page from host B to declare
   that its content (for example example, a button, links, text, etc.) must not
   be displayed in a frame (<frame> or <iframe>) of another page (e.g. (e.g.,
   from host A).  This is done by a policy declared in the HTTP header
   and enforced by browser implementations as documented here.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  X-Frame-Options Header

   The X-Frame-Options HTTP response header field indicates a policy on that
   specifies whether the browser should render the transmitted resource
   within a <frame> or an <iframe>.  Servers can declare this policy in
   the header of their HTTP responses to prevent clickjacking attacks, and by this
   ensuring
   which ensures that their content is not embedded into other pages or
   frames.

2.1.  Syntax

   The header field name is:

      X-Frame-Options

   There are three different values for the header field.  These values
   are mutually exclusive, exclusive; that is is, the header field MUST be set to
   exactly one of the three values MUST
   be set. values.

   DENY
      A browser receiving content with this header field MUST NOT
      display this content in any frame.

   SAMEORIGIN
      A browser receiving content with this header field MUST NOT
      display this content in any frame from a page of different origin
      than the content itself.

      If a browser or plugin can not cannot reliably determine whether or not
      the origin of the content and the frame have are the same origin, same, this MUST be
      treated as "DENY".

      Please note that current implementations vary on the
      interpretation of this criteria: criteria.  In some some, it only allows a page
      to be framed if the origin of the top-level browsing-context browsing context is
      identical to the origin of the content using the X-FRAME-
         OPTIONS X-Frame-Options
      directive; in others others, it may consider the origin of the framing
      page instead.  See also section  Also see Section 2.3.2.2 for more details on the
      nesting of frames and variations in the handling of this header
      field by different browsers.  And  In addition, refer to
         section 5 Section 4,
      paragraph 2 for the resulting potential security problems.

   ALLOW-FROM  (followed by a serialized-origin [RFC6454])
      A browser receiving content with this header MUST NOT display this
      content in a frame from any page with a top-level browsing context
      of different origin than the specified origin.  While this can
      expose the page to risks by the trusted origin, in some cases cases, it
      may be necessary to allow the framing by content from other
      domains.

   The meaning of the term "serialized-origin" is given in [RFC6454].
   If the ALLOW-FROM value is used, it MUST be followed by a valid
   origin [RFC6454] (as a subset of the URI [RFC3986]) [RFC3986]).

   Any data beyond the domain address (i.e. (i.e., any data after the "/"
   separator) is to be ignored.  And the  The algorithm to compare origins from
   [RFC6454] SHOULD be used to verify that a referring page is of the
   same origin as the content (in the case of SAMEORIGIN) or that the
   referring page's origin is identical with the ALLOW-FROM
   serialized-origin serialized-
   origin (in the case of ALLOW-FROM).  Though in conflict with
   [RFC6454], current implementations do not consider the port as a
   defining component of the origin.  I.e. origin; i.e., existing implementations
   differ with [RFC6454] in that origins with the same protocol but
   different port values are considered equivalent.

   Wildcards or lists to declare multiple domains in one ALLOW-FROM
   statement are not permitted (see Section 2.3.2.3).

2.2.   Augmented Backus-Naur Form (ABNF)

   The RFC 5234 [RFC5234] ABNF of the X-Frame-Options header field value
   is the following. following:

         X-Frame-Options = "DENY"
                   / "SAMEORIGIN"
                   / ( "ALLOW-FROM" RWS SERIALIZED-ORIGIN )

         RWS             = 1*( SP / HTAB )
                       ; required whitespace

   With

   with serialized-origin as defined in [RFC6454] and the definition of
   RWS (required whitespace) is the same required
   whitespace (RWS) as defined in [HTTPbis-P1].

   RWS is used when at least one linear whitespace octet is required to
   separate field tokens.  RWS SHOULD be generated as a single space
   (SP).  Multiple RWS octets that occur within field-content SHOULD
   either be replaced with a single SP or transformed to all SP octets before
   interpreting the field value or forwarding the message downstream.

   And

   SP (space) and HTAB (horizontal tab) horizontal tab (HTAB) are as defined in Appendix B.1 of RFC
   5234
   [RFC5234], Appendix B.1. [RFC5234].

   The values are specified as ABNF strings, and therefore strings; therefore, they are case-
   insensitive.

2.2.1.  Examples of X-Frame-Options

       X-FRAME-OPTIONS:

       X-Frame-Options: DENY

       X-FRAME-OPTIONS:

       X-Frame-Options: SAMEORIGIN

       X-FRAME-OPTIONS:

       X-Frame-Options: ALLOW-FROM https://example.com/

2.3.  Design Issues

2.3.1.  Enable HTML content Content from other domains Other Domains

   There are a number of main direct vectors that enable HTML content
   from other domains domains, and browser implementations of X-Frame-Options
   cover all of them:

   o  IFRAME tag

   o  Frame tag

   o  The  Object tag (requires a redirect)

   o  Applet tag

   o  Embed tag

   Besides these, other ways to host HTML content can be possible.  For
   example
   example, some plugins may host HTML views directly.  If these plugins
   appear essentially as frames (as opposed to top-level windows), the
   plugins must conform to the X-FRAME-OPTIONS X-Frame-Options policy as specified in
   this document as well.

2.3.2.  Browser Behaviour Behavior and Processing

   To allow secure implementations, browsers must behave in a consistent
   and reliable way.

   If an X-Frame-Options HTTP header field prohibits framing, the user- user
   agent of the browser MAY immediately abort downloading or parsing of
   the document.

2.3.2.1.  Violation of X-Frame-Options

   When a browser discovers that loaded content with the X-FRAME-OPTIONS X-Frame-Options
   header field would be displayed in a frame against the specified
   orders of the header, the browser SHOULD redirect to a "NOFRAME" page
   as soon as possible
   to a "No-Frame" page. possible.  For example example, this can be a noframe.html page
   that also states the full URL and hostname of the protected page.

   The NoFrame NOFRAME page could provide the user with an option to open the
   target URL in a new window.

   Implementations of this vary, vary: some browsers will show a message that
   allows the user to safely open the target page in a new window.
   Other window,
   whereas other implementations will simply render an empty frame.

2.3.2.2.  Variation in current browser behaviour Current Browser Behavior

   There are currently variations in the implementation of the X-FRAME-
   OPTIONS
   X-Frame-Options header.  For example example, not all browsers support the "ALLOW-
   FROM"
   "ALLOW-FROM" option.  "ALLOW-FROM" was initially an Internet Explorer
   extension and and, at the time of writing writing, has not been uniformly
   implemented by other user agents.

   Furthermore

   Furthermore, the criteria for the SAMEORIGIN (and ALLOW-FROM)
   directive may not be evaluated unanimously either: The the known
   implementations in Appendix A evaluate the SAMEORIGIN directive based
   on the origin of the framed page and the top-level browsing-context, browsing context,
   while other implementations might evaluate it based on the framed
   page and the framing page, or the whole chain of nested frames inbetween. in
   between.

   To illustrate the difference between the comparison with of the "framing
   page" and the "top-level browsing-context" browsing context", consider the following
   scenario: Web web pages may embed frames with other pages which that, in turn turn,
   embed frames with other pages as well well, and so on.  In theory theory, this
   can result in an infinite nesting of framed pages.  For example example, web
   page A may contain in a frame web page B, B in a frame, and web page B contains in a
   frame may contain
   web page C. C in a frame.

   Web page A
   <html>
   ....
   <frame src="https://URI_of_web_page_B" />
   </html>

   Web Page page B
   <html>
   ....
   <frame src="https://URI_of_web_page_C" />
   </html>

   And

   and so forth... forth.

   In this example, for the nested frames with the inner framed inner-framed web page
   C, the most outer web page A would be the "top-level browsing-
   context" browsing
   context", and web page B would be the "framing page" page".

   These potential variations in the evaluation of the header by
   different implementations impair the useage usage and reliability of this
   http
   HTTP header and have security implications as described in section 5. Section 4.
   A revised version of x-frame-options X-Frame-Options in the form of a frame-options Frame-Options
   directive in the CSP 1.1[CSP-1-1] 1.1 [CSP-1-1] will unify the behaviour behavior, and it is
   expected that newer implementations will use it rather than the
   mechanisms documented here.

2.3.2.3.  Usage design pattern Design Pattern and example scenario Example Scenario for the ALLOW-FROM
          parameter
          Parameter

   As the "ALLOW-FROM" field only supports one serialized-origin, in
   cases when the server wishes to allow more than one resource to frame
   its content, the following design pattern can fulfil fulfill that need:

   1.  A page that wants to render the requested content in a frame
       supplies its own origin information to the server providing the
       to-be-framed
       content to be framed via a querystring query string parameter.

   2.  The Server server verifies that the hostname meets its criteria criteria, so that
       the page can be is allowed to be framed by the target resource.  This
       may
       may, for example example, happen via a look-up lookup of a white-list whitelist of trusted
       domain names that are allowed to frame the page.  For example,
       for a Facebook "Like" button, the server can check to see that
       the supplied hostname matches the hostname(s) expected for that
       "Like" button.

   3.  The server returns the hostname in X-FRAME-OPTIONS: ALLOW-FROM "X-Frame-Options: ALLOW-FROM"
       if the proper criteria was met in step #2.

   4.  The browser enforces the X-FRAME-OPTIONS: ALLOW-FROM "X-Frame-Options: ALLOW-FROM" header.

2.3.2.4.  No caching Caching of the X-Frame-Options header

   It is not recommended to cache Header

   Caching the X-Frame-Options header for a
   resource. resource is not recommended.
   Caching the X-Frame-Options response could result in problems
   because:

   1.  The browser has to check for  For every http-request of the resource resource, the browser has to check
       whether the X-Frame-Options header has been set and then act
       accordingly, as a resource itself might be created dynamically
       and the header could change with it, too.

   2.  And also,  Also, as outlined in section 2.3.2.3., Section 2.3.2.3, servers may generate X
       -Frame-Options
       X-Frame-Options header responses depending on the request.
       Example case: Considering that we have only one serialized-origin
       in the ALLOW-FROM directive, imagine a user has multiple pages
       open in his browser tabs with one of web page 1 from domain A and
       the second of web
       page 2 from domain B, and both frame the same page from domain C
       with the ALLOW-FROM directive.  In that case case, the page needs to
       reply to both requests with different X-Frame-
       Options X-Frame-Options headers,
       with the first pointing to origin A, A and the second pointing to
       origin B.

   However, we found that none of the major browsers listed in
   Appendix A cache the responses.

3.  Acknowledgements

   This document was derived from input from specifications published by
   various browser vendors such as Microsoft (Eric Lawrence, David
   Ross), Mozilla, Google, Opera and Apple.

4.  IANA Considerations

   This memo is a request to

   IANA to include has included the specified HTTP header in the "Permanent Message
   Header Field Name" registry as outlined in Registration "Registration Procedures
   for Message Header Fields [RFC3864]

4.1. Fields" [RFC3864].

3.1.  Registration Template

   PERMANENT MESSAGE HEADER FIELD REGISTRATION TEMPLATE:

   Permanent Message Header Field Names Template:

   Header field name: X-Frame-Options

   Applicable protocol: http [RFC2616]

   Status: informational

   Author/Change Informational

   Author/change controller: IETF

   Specification document(s): draft-ietf-websec-x-frame-options RFC 7034

   Related information:

                                 Figure 1

5. None

4.  Security Considerations

   The introduction of the X-FRAME-OPTIONS http X-Frame-Options HTTP header field does
   improve improves
   the protection against Clickjacking. clickjacking.  However, it is not
   self-sufficient on its own self-
   sufficient enough to protect against all kinds of these attack
   vectors.  It must be used in conjunction with other security measures
   like secure coding (e.g. (e.g., input validation, output encoding,
   ...) etc.)
   and the Content Security Policy version 1.0 [CSP].

   It is important to note that current implementations do not check the
   origins of the framing resources' entire ancestor tree of frames of the framing
   resources, frames, and
   this may expose the resource to attack in multiple-
   nested multiple-nested scenarios.

   The browser implementations evaluate based on the origin of the
   framed page and the top-level browsing-context (i.e. browsing context (i.e., the most outer
   frame):

   If a resource from origin A embeds untrusted content from origin B,
   that untrusted content can embed another resource from origin A with
   an X-Frame-Options: SAMEORIGIN policy "X-Frame-Options: SAMEORIGIN" policy, and that check would pass
   when the user agent only verifies the top-level browsing context.
   Therefore
   Therefore, web developers should be aware that embedding content from
   other sites can leave their web pages vulnerable to clickjacking even
   if the X-Frame-Options header is used.

   Furthermore, X-Frame-Options must be sent as an HTTP header field and
   is explicitly ignored by user agents when declared with a meta http-
   equiv
   http-equiv tag.

5.1.

4.1.  Privacy Considerations

   There are two kinds of potential data leakage to consider:

   1.  Using X-FRAME-OPTIONS X-Frame-Options with the parameter ALLOW-FROM allows a page
       to guess or infer information about who is framing it.  A web
       server may answer requests with the X-FRAME-OPTIONS ALLOW-FROM "X-Frame-Options: ALLOW-FROM"
       header and by thus determine which other page is framing it.  This
       is inherent by design, but it may lead to data leakage data-leakage or data data-
       protection concerns.

   2.  The web server using the ALLOW-FROM directive may disclose to
       other parties who request effectively
       discloses the page origin specified in the header by which page it
       is allowed to be framed. header.  If a web server
       wishes to reduce this leakage, it is recommended to generate the
       ALLOW-FROM header for each request based on the design pattern as
       described in section Section 2.3.2.3.

6.

5.  References

6.1.

5.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC6454]  Barth, A., "The Web Origin Concept", RFC 6454,
              December 2011.

6.2.

5.2.  Informative References

   [CLICK-DEFENSE-BLOG]
              Microsoft, "Clickjacking Defense", 2009, <http://
              blogs.msdn.com/b/ie/archive/2009/01/27/ie8-security-part-
              vii-clickjacking-defenses.aspx>.

   [CSP-1-1]  Barth, A. and M. West, "Content
              Lawrence, E., "IE8 Security Policy 1.1", W3C
              Working Draft WD-CSP11-20130604, June 2013,
              <http://www.w3.org/TR/2013/WD-CSP11-20130604/>.

              Latest version available at Part VII: Clickjacking
              Defenses", Microsoft Developer Network Blogs,
              January 2009, <http://blogs.msdn.com/b/ie/archive/2009/01/
              27/ie8-security-part-vii-clickjacking-defenses.aspx>.

   [CSP]      Sterne, B. and A. Barth, "Content Security Policy 1.0",
              W3C Candidate Recommendation CR-CSP-20121115,
              November 2012,
              <http://www.w3.org/TR/2012/CR-CSP-20121115/>.

              Latest version available at

   [CSP-1-1]  Barth, A. and M. West, "Content Security Policy 1.1", W3C
              Working Draft WD-CSP11-20130604, June 2013,
              <http://www.w3.org/TR/2013/WD-CSP11-20130604/>.

   [CSRF]     OWASP (Open Web Application Security Project), "OWASP
              Top-10: Cross-Site "Top-10
              2013-A8-Cross-Site Request Forgery (CSRF)", 2010, <https:/
              /www.owasp.org/index.php/Top_10_2013-A8-Cross-
              Site_Request_Forgery_%28CSRF%29>. June 2013,
              <https://www.owasp.org/index.php/
              Top_10_2013-A8-Cross-Site_Request_Forgery_%28CSRF%29>.

   [Clickjacking]
              OWASP (Open Web Application Security Project),
              "Clickjacking", 2010, April 2013,
              <http://www.owasp.org/index.php/Clickjacking>.

   [FRAME-BUSTING]
              Stanford Web Security Research, "Busting frame busting: a
              study of clickjacking vulnerabilities at popular sites",
              July 2010,
              <http://seclab.stanford.edu/websec/framebusting/>.

   [HTTPbis-P1]
              IETF,
              Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Message Syntax and Routing", 2013, <http://tools.ietf.org/html/
              draft-ietf-httpbis-p1-messaging-23>. Work in Progress,
              July 2013.

   [Microsoft-X-Frame-Options]
              Microsoft,
              Lawrence, E., "Combating ClickJacking With X-Frame-Options", X-Frame-
              Options", Microsoft Developer Network Blogs, March 2010, <http://blogs.msdn.com/b/ieinternals/archive/2010/03
              /30/combating-clickjacking-with-x-frame-options.aspx>.
              <http://blogs.msdn.com/b/ieinternals/archive/2010/03/30/
              combating-clickjacking-with-x-frame-options.aspx>.

   [Mozilla-X-Frame-Options]
              Mozilla,
              Mozilla Developer Network, "The X-Frame-Options response
              header", 2010,
              <https://developer.mozilla.org/en-US/docs/The_X-FRAME-
              OPTIONS_response_header>. August 2013, <https://developer.mozilla.org/
              en-US/docs/The_X-FRAME-OPTIONS_response_header>.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
              Procedures for Message Header Fields", BCP 90, RFC 3864,
              September 2004.

   [RFC6648]  Saint-Andre, P., Crocker, D., and M. Nottingham,
              "Deprecating the "X-" Prefix and Similar Constructs in
              Application Protocols", BCP 178, RFC 6648, June 2012.

Appendix A.  Browsers that support That Support X-Frame-Options

   o  Internet Explorer 8+

   o  Firefox 3.6.9+

   o  Opera 10.5+

   o  Safari 4+

   o  Chrome 4.1+

Appendix B.  Description of a Clickjacking attack

   More Attack

   A more detailed explanation of Clickjacking clickjacking scenarios follows.

B.1.  Shop

   An Internet Marketplace/Shop marketplace/shop offering a feature with a link/button to
   "Buy this" Gadget
   The marketplace gadget wants their affiliates (who could be malicious
   attackers) to be able to stick the "Buy such-and-such such and such from XYZ"
   IFRAMES into their pages.  There is a possible Clickjacking clickjacking threat
   here, which is why the marketplace/onlineshop marketplace/online shop needs to then
   immediately navigate the main browsing context (or a new window) to a
   confirmation page which that is protected by anti-Clickjacking anti-clickjacking protections.

B.2.  Online Shop Confirm Purchase Page

   The "Confirm Purchase" page of an online shop must be shown to the
   end user
   end-user without the risk of an overlay or misuse by an attacker.
   For that reason, the confirmation page uses a combination of anti-
   CSRF
   anti-CSRF (Cross Site Request Forgery, Forgery [CSRF]) tokens and the X-FRAME-
   OPTIONS
   X-Frame-Options HTTP header field, mitigating ClickJacking clickjacking attacks.

B.3.  Flash Configuration

   Macromedia Flash configuration settings are set by a Flash object
   which
   that can run only from a specific configuration page on Macromedia's
   site.  The object runs inside the page and thus can be subject to a
   ClickJacking
   clickjacking attack.  In order to prevent ClickJacking clickjacking attacks
   against the security settings, the configuration page uses the X
   -FRAME-OPTIONS
   X-Frame-Options directive.

Appendix C.  Acknowledgements

   This document was derived from input from specifications published by
   various browser vendors such as Microsoft (Eric Lawrence and David
   Ross), Mozilla, Google, Opera, and Apple.

Authors' Addresses

   David Ross
   Microsoft
   U.S.

   EMail: dross@microsoft.com

   Tobias Gondrom
   Thames Stanley
   Kruegerstr. 5A
   Unterschleissheim
   Germany

   Phone: +44 7521003005
   Email:

   EMail: tobias.gondrom@gondrom.org