Internet Engineering Task Force (IETF) D. Ross Request for Comments: 7034 Microsoft Category: Informational T. Gondrom ISSN: 2070-1721 Thames Stanley October 2013 HTTP Header Field X-Frame-Options Abstract To improve the protection of web applications against clickjacking, this document describes the X-Frame-Options HTTP header field, which declares a policy, communicated from the server to the client browser, regarding whether the browser may display the transmitted content in frames that are part of other web pages. Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of 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 candidate for any level of Internet Standard; see Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7034. Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Ross & Gondrom Informational [Page 1] RFC 7034 X-Frame-Options October 2013 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. X-Frame-Options Header . . . . . . . . . . . . . . . . . . . . 4 2.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Augmented Backus-Naur Form (ABNF) . . . . . . . . . . . . 5 2.2.1. Examples of X-Frame-Options . . . . . . . . . . . . . 6 2.3. Design Issues . . . . . . . . . . . . . . . . . . . . . . 6 2.3.1. Enable HTML Content from Other Domains . . . . . . . . 6 2.3.2. Browser Behavior and Processing . . . . . . . . . . . 6 2.3.2.1. Violation of X-Frame-Options . . . . . . . . . . . 6 2.3.2.2. Variation in Current Browser Behavior . . . . . . 7 2.3.2.3. Usage Design Pattern and Example Scenario for the ALLOW-FROM Parameter . . . . . . . . . . . . . 8 2.3.2.4. No Caching of the X-Frame-Options Header . . . . . 8 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 3.1. Registration Template . . . . . . . . . . . . . . . . . . 9 4. Security Considerations . . . . . . . . . . . . . . . . . . . 9 4.1. Privacy Considerations . . . . . . . . . . . . . . . . . . 10 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.1. Normative References . . . . . . . . . . . . . . . . . . . 10 5.2. Informative References . . . . . . . . . . . . . . . . . . 11 Appendix A. Browsers That Support X-Frame-Options . . . . . . . . 13 Appendix B. Description of a Clickjacking Attack . . . . . . . . 13 B.1. Shop . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 B.2. Online Shop Confirm Purchase Page . . . . . . . . . . . . 13 B.3. Flash Configuration . . . . . . . . . . . . . . . . . . . 13 Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 13 Ross & Gondrom Informational [Page 2] RFC 7034 X-Frame-Options October 2013 1. Introduction In 2009 and 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]. 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 page A and routing them to 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. 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, not all browsers implement X-Frame-Options in exactly the same way, which can lead to unintended results. And, given that the "X-" construction is deprecated [RFC6648], the X-Frame-Options header field will be replaced in the future by the Frame-Options directive in the Content Security Policy (CSP) version 1.1 [CSP-1-1]. A study [FRAME-BUSTING] demonstrated that existing anti-clickjacking measures, e.g., frame-breaking JavaScript, have weaknesses that allow their protection to be circumvented. Short of configuring the browser to disable frames and 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, a button, links, text, etc.) must not be displayed in a frame ( or