idnits 2.17.1 

draft-ietf-websec-x-frame-options-04.txt:

  Checking boilerplate required by RFC 5378 and the IETF Trust (see
  https://trustee.ietf.org/license-info):
  ----------------------------------------------------------------------------

     No issues found here.

  Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt:
  ----------------------------------------------------------------------------

     No issues found here.

  Checking nits according to https://www.ietf.org/id-info/checklist :
  ----------------------------------------------------------------------------

     No issues found here.

  Miscellaneous warnings:
  ----------------------------------------------------------------------------

  == The copyright year in the IETF Trust and authors Copyright Line does not
     match the current year

  -- The document date (June 28, 2013) is 3948 days in the past.  Is this
     intentional?


  Checking references for intended status: Informational
  ----------------------------------------------------------------------------

  == Outdated reference: A later version (-26) exists of
     draft-ietf-httpbis-p1-messaging-22

  -- Obsolete informational reference (is this intentional?): RFC 2616
     (Obsoleted by RFC 7230, RFC 7231, RFC 7232, RFC 7233, RFC 7234, RFC 7235)


     Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--).

     Run idnits with the --verbose option for more detailed information about
     the items above.
--------------------------------------------------------------------------------


2	WEBSEC                                                           D. Ross
3	Internet-Draft                                                 Microsoft
4	Intended status: Informational                                T. Gondrom
5	Expires: December 30, 2013                                Thames Stanley
6	                                                           June 28, 2013

8	                   HTTP Header Field X-Frame-Options
9	                  draft-ietf-websec-x-frame-options-04

11	Abstract

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

21	Status of This Memo

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

26	   Internet-Drafts are working documents of the Internet Engineering
27	   Task Force (IETF).  Note that other groups may also distribute
28	   working documents as Internet-Drafts.  The list of current Internet-
29	   Drafts is at http://datatracker.ietf.org/drafts/current/.

31	   Internet-Drafts are draft documents valid for a maximum of six months
32	   and may be updated, replaced, or obsoleted by other documents at any
33	   time.  It is inappropriate to use Internet-Drafts as reference
34	   material or to cite them other than as "work in progress."

36	   This Internet-Draft will expire on December 30, 2013.

38	Copyright Notice

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

43	   This document is subject to BCP 78 and the IETF Trust's Legal
44	   Provisions Relating to IETF Documents
45	   (http://trustee.ietf.org/license-info) in effect on the date of
46	   publication of this document.  Please review these documents
47	   carefully, as they describe your rights and restrictions with respect
48	   to this document.  Code Components extracted from this document must
49	   include Simplified BSD License text as described in Section 4.e of
50	   the Trust Legal Provisions and are provided without warranty as
51	   described in the Simplified BSD License.

53	Table of Contents

55	   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
56	     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
57	   2.  X-Frame-Options Header  . . . . . . . . . . . . . . . . . . .   3
58	     2.1.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . .   3
59	     2.2.   Augmented Backus-Naur Form (ABNF)  . . . . . . . . . . .   4
60	       2.2.1.  Examples of X-Frame-Options . . . . . . . . . . . . .   5
61	     2.3.  Design Issues . . . . . . . . . . . . . . . . . . . . . .   5
62	       2.3.1.  Enable HTML content from other domains  . . . . . . .   5
63	       2.3.2.  Browser Behaviour and Processing  . . . . . . . . . .   5
64	         2.3.2.1.  Violation of X-Frame-Options  . . . . . . . . . .   5
65	         2.3.2.2.  Variation in current browser behaviour  . . . . .   6
66	         2.3.2.3.  Usage design pattern and example scenario for the
67	                   ALLOW-FROM parameter  . . . . . . . . . . . . . .   6
68	   3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
69	   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
70	     4.1.  Registration Template . . . . . . . . . . . . . . . . . .   7
71	   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
72	     5.1.  Privacy Considreations  . . . . . . . . . . . . . . . . .   8
73	   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
74	     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
75	     6.2.  Informative References  . . . . . . . . . . . . . . . . .   9
76	   Appendix A.  Browsers that support X-Frame-Options  . . . . . . .  10
77	   Appendix B.  Description of a Clickjacking attack . . . . . . . .  10
78	     B.1.  Shop  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
79	     B.2.  Online Shop Confirm Purchase Page . . . . . . . . . . . .  10
80	     B.3.  Flash Configuration . . . . . . . . . . . . . . . . . . .  10
81	   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

83	1.  Introduction

85	   In 2009 and 2010 many browser vendors ([Microsoft-X-Frame-Options],
86	   [CLICK-DEFENSE-BLOG], [Mozilla-X-Frame-Options]) introduced the use
87	   of a non-standard HTTP [RFC2616] header field "X-Frame-Options" to
88	   protect against Clickjacking Clickjacking [Clickjacking].  HTML-based
89	   web applications can embed or "frame" other web pages.  Clickjacking
90	   is a type of attack that occurs when an attacker uses multiple
91	   transparent or opaque layers in the user interface to trick a user
92	   into clicking on a button or link on another page from server B when
93	   they were intending to click on the same place of the overlaying page
94	   from server A.  Thus, the attacker is "hijacking" clicks meant for
95	   their page A and routing them to another page B, possibly belonging
96	   to another domain and thereby triggering actions on the second server
97	   B without the knowledge nor intention of the user and potentially
98	   using an existing session context and login in that step.

100	   This specification provides informational documentation about the
101	   current use and definition of the X-Frame-Options HTTP header field.
102	   Given that the "X-" construction is deprecated [RFC6648], the X
103	   -Frame-Options header field will in the future be replaced by the
104	   Frame-Options directive in the Content Security Policy Version 1.1
105	   [CSP-1-1].

107	   Existing anti-ClickJacking measures, e.g.  Frame-breaking Javascript,
108	   have weaknesses so that their protection can be circumvented as a
109	   study [FRAME-BUSTING] demonstrated.

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

115	   "X-Frame-Options" allows a secure web page from host B to declare
116	   that its content (for example a button, links, text, etc.) must not
117	   be displayed in a frame (<frame> or <iframe>) of another page (e.g.
118	   from host A).  In principle this is done by a policy declared in the
119	   HTTP header and enforced by conforming browser implementations.

121	1.1.  Requirements Language

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

127	2.  X-Frame-Options Header

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

136	2.1.  Syntax

138	   The header field name is:
139	   X-Frame-Options

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

145	   DENY
146	         A browser receiving content with this header MUST NOT display
147	         this content in any frame.

149	   SAMEORIGIN
150	         A browser receiving content with this header field MUST NOT
151	         display this content in any frame from a page of different
152	         origin than the content itself.
153	         If a browser or plugin can not reliably determine whether the
154	         origin of the content and the frame have the same origin, this
155	         MUST be treated as "DENY".
156	         Please note that current implementations vary on the
157	         interpretation of this criteria: In some it only allows to be
158	         framed if the origin of the top-level browsing-context is
159	         identical to the origin of the content using the X-FRAME-
160	         OPTIONS directive, in others it may compare to the origin of
161	         the framing page.

163	   ALLOW-FROM  (followed by a URI [RFC3986] of a trusted origin)
164	         A browser receiving content with this header MUST NOT display
165	         this content in a frame from any page with a top-level browsing
166	         context of different origin than the specified origin.  While
167	         this can expose the page to risks by the trusted origin, in
168	         some cases it may be necessary to allow the framing by content
169	         from other domains.

171	   If the ALLOW-FROM value is used, it MUST be followed by a valid URI.
172	   Any data beyond the domain address (i.e. any data after the "/"
173	   separator) is to be ignored.  And the algorithm to compare origins
174	   from [RFC6454] SHOULD be used to verify that a referring page is of
175	   the same origin as the content or that the referring page's origin is
176	   identical with the ALLOW-FROM URI.  Though in conflict with
177	   [RFC6454], current implementations do not consider the port as a
178	   defining component of the origin.

180	   Wildcards or lists to declare multiple domains in one ALLOW-FROM
181	   statement are not permitted.

183	2.2.  Augmented Backus-Naur Form (ABNF)

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

188	      X-Frame-Options = "DENY"
189	                / "SAMEORIGIN"
190	                / ( "ALLOW-FROM" RWS URI )

192	   With URI as defined in [RFC3986] and RWS and OWS as defined in
193	   [HTTPbis-P1].  The values are specified as ABNF strings, and
194	   therefore are case-insensitive.

196	2.2.1.  Examples of X-Frame-Options

198	       X-FRAME-OPTIONS: DENY

200	       X-FRAME-OPTIONS: SAMEORIGIN

202	       X-FRAME-OPTIONS: ALLOW-FROM https://example.com/

204	2.3.  Design Issues

206	2.3.1.  Enable HTML content from other domains

208	   There are a number of main direct vectors that enable HTML content
209	   from other domains:

211	   o  IFRAME tag

213	   o  Frame tag

215	   o  The Object tag (requires a redirect)

217	   o  Applet tag

219	   o  Embed tag

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

227	2.3.2.  Browser Behaviour and Processing

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

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

236	2.3.2.1.  Violation of X-Frame-Options
237	   When a browser discovers that loaded content with the X-FRAME-OPTIONS
238	   header field would be displayed in a frame against the specified
239	   orders of the header, the browser SHOULD redirect as soon as possible
240	   to a "No-Frame" page.

242	   "No-Frame" Page
243	   If the display of content is denied by the X-FRAME-OPTIONS header an
244	   error page SHOULD be displayed.  For example this can be a
245	   noframe.html page also stating the full URL of the protected page and
246	   the hostname of the protected page.

248	   The NoFrame page MAY provide the user with an option to open the
249	   target URL in a new window.

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

255	2.3.2.2.  Variation in current browser behaviour

257	   There are currently variations in the implementation of the X-FRAME-
258	   OPTIONS header.  For example not all browsers support the "ALLOW-
259	   FROM" option.  "ALLOW-FROM" was initially an IE (Internet Explorer)
260	   extension and at the time of writing has not been uniformly
261	   implemented by other user agents.

263	   And the criteria for the SAMEORIGIN option is not evaluated
264	   unanimously either: one implementation may evaluate the SAMEORIGIN
265	   option based on the origin of the framed page and the framing page,
266	   while another may evaluate based on the framed page and the top-level
267	   browsing-context.

269	   These variations in the evaluation of the header by different
270	   implementations impair the useage and reliability of this http
271	   header.  A revised version of x-frame-options in the form of a frame-
272	   options directive in the CSP 1.1[CSP-1-1] shall unify the behaviour
273	   and replace this document in the future.

275	2.3.2.3.  Usage design pattern and example scenario for the ALLOW-FROM
276	          parameter

278	   As the "ALLOW-FROM" field does support only one URI, in cases when
279	   the server wishes to allow more than one resource to frame its
280	   content, the following design pattern is recommended:

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

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

294	   3.  The server return the hostname in X-FRAME-OPTIONS: ALLOW-FROM if
295	       the proper criteria was met in step #2.

297	   4.  The browser enforces the X-FRAME-OPTIONS: ALLOW-FROM header.

299	3.  Acknowledgements

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

305	4.  IANA Considerations

307	   This memo is a request to IANA to include the specified HTTP header
308	   in the registry as outlined in Registration Procedures for Message
309	   Header Fields [RFC3864]

311	4.1.  Registration Template

313	   PERMANENT MESSAGE HEADER FIELD REGISTRATION TEMPLATE:

315	   Header field name: X-Frame-Option

317	   Applicable protocol: http [RFC2616]

319	   Status: Standard

321	   Author/Change controller: IETF

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

325	   Related information:

327	                                 Figure 1

329	5.  Security Considerations

331	   The introduction of the X-FRAME-OPTIONS http header field does
332	   improve the protection against Clickjacking.  However, it is not
333	   self-sufficient on its own, but must be used in conjunction with
334	   other security measures like secure coding and the Content Security
335	   Policy [CSP].

337	   It is important to note that current implementations do not check the
338	   origins of the entire ancestor tree of frames of the framing
339	   resources, and this may expose the resource to attack in multiply-
340	   nested scenarios.  For example, if a resource on origin A embeds
341	   untrusted content from origin B, that untrusted content can embed
342	   another resource from origin A with an X-Frame-Options: SAMEORIGIN
343	   policy and that check would pass if the user agent only verifies the
344	   top-level browsing context.

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

350	5.1.  Privacy Considreations

352	   The parameter ALLOW-FROM allows a page to guess who is framing it.
353	   This is inherent by design, but may lead to data leakage or data
354	   protection concerns.

356	6.  References

358	6.1.  Normative References

360	   [HTTPbis-P1]
361	              IETF, "Hypertext Transfer Protocol (HTTP/1.1): Message
362	              Syntax and Routing", 2013, <http://tools.ietf.org/html/
363	              draft-ietf-httpbis-p1-messaging-22>.

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

368	   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
369	              Resource Identifier (URI): Generic Syntax", STD 66, RFC
370	              3986, January 2005.

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

375	   [RFC6454]  Barth, A., "The Web Origin Concept", RFC 6454, December
376	              2011.

378	6.2.  Informative References

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

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

389	              Latest version available at

391	   [CSP]      Sterne, B. and A. Barth, "Content Security Policy 1.0",
392	              W3C Candidate Recommendation CR-CSP-20121115, November
393	              2012, <http://www.w3.org/TR/2012/CR-CSP-20121115/>.

395	              Latest version available at

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

402	   [FRAME-BUSTING]
403	              Stanford Web Security Research, "Busting frame busting: a
404	              study of clickjacking vulnerabilities at popular sites",
405	              2010, <http://seclab.stanford.edu/websec/framebusting/>.

407	   [Microsoft-X-Frame-Options]
408	              Microsoft, "Combating ClickJacking With X-Frame-Options",
409	              2010, <http://blogs.msdn.com/b/ieinternals/archive/2010/03
410	              /30/combating-clickjacking-with-x-frame-options.aspx>.

412	   [Mozilla-X-Frame-Options]
413	              Mozilla, "The X-Frame-Options response header", 2010,
414	              <https://developer.mozilla.org/en-US/docs/The_X-FRAME-
415	              OPTIONS_response_header>.

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

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

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

429	Appendix A.  Browsers that support X-Frame-Options

431	   o  Internet Explorer 8+

433	   o  Firefox 3.6.9+

435	   o  Opera 10.5+

437	   o  Safari 4+

439	   o  Chrome 4.1+

441	Appendix B.  Description of a Clickjacking attack

443	   More detailed explanation of Clickjacking scenarios

445	B.1.  Shop

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

457	B.2.  Online Shop Confirm Purchase Page

459	   The "Confirm Purchase"" page of an online shop must be shown to the
460	   end user without the risk of an overlay or misuse by an attacker.
461	   For that reason, the confirmation page uses a combination of anti-
462	   CSRF tokens and the X-FRAME-OPTIONS HTTP header field, mitigating
463	   ClickJacking attacks.

465	B.3.  Flash Configuration

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

474	Authors' Addresses

476	   David Ross
477	   Microsoft
478	   U.S.

480	   Tobias Gondrom
481	   Thames Stanley
482	   Kruegerstr. 5A
483	   Unterschleissheim
484	   Germany

486	   Phone: +44 7521003005
487	   Email: tobias.gondrom@gondrom.org