HTTP Header Frame Options
draft-gondrom-frame-options-00

Abstract

To improve the protection of web applications against Cross Site Request Forgery (CSRF) and Clickjacking this standards defines a http response header that declares a policy communicated from a host to the client browser whether the transmitted content MUST NOT be displayed in frames of other pages from different origins or a list of trusted origins which are allowed to frame the content.

Status of this Memo

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

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

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This Internet-Draft will expire on September 08, 2011.

Copyright Notice

Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 1.1. Requirements Language
• 2. Frame-Options Header
• 2.1. Syntax
• 2.2. Backus-Naur Form (BNF)
• 2.3. Examples of Frame-Options Headers
• 3. Acknowledgements
• 4. IANA Considerations
• 4.1. Registration Template
• 5. Security Considerations
• 6. References
• 6.1. Normative References
• 6.2. Informative References
• Appendix A. Description of a Clickjacking attack
• Authors' Addresses

1. Introduction

In 2009 and 2010 many browser vendors introduced the use of a non-standard http header RFC 2616 [RFC2616] "X-Frame-Options" to protect against Clickjacking [Clickjacking] and Cross Site Request Forgery (CSRF) [CSRF]. This standard is to replace the non-standard header.

With Clickjacking and CSRF an attacker tricks a user into clicking on a button or link to another page and by thus executing an unintended command in the context of a different web application. For example with Clickjacking the attacker might use transparent or opaque layers to integrate and obscure a button to another page so that the user may click on it in the expectation of a different action. So, in this way the attacker is "hijacking" the "Click" on a button meant by the user to be sent to host A, while clicking the button in effect sends a message to host B. If the user does for example also have an open session with host B this can lead to a CSRF attack and executing a command in the session context of the user (using the user's authentication and authorization) on host B without his intention or knowledge.

The by "Frame-Options" provided defense mechanism against Clickjacking is to allow a secure web page from host B to declare that its content (for example a button, links, text, etc.) must not be displayed in a frame of another page (e.g. from host A). In principle this is done by a policy declared in the HTTP header and obeyed by conform browser implementations.

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. Frame-Options Header

The Frame-Options HTTP response header indicates a policy whether a browser MUST NOT allow to render a page in a <frame> or <iframe> . Hosts can declare this policy in the header of their HTTP responses to prevent clickjacking attacks, by ensuring that their content is not embedded into other pages or frames.

2.1. Syntax

The header field name is:

Frame-Options

There are three different values for the header field. These values are exclusive, that is NOT more than one of the three values MUST be set.

DENY

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

SAMEORIGIN

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

TRUSTED

(followed by a list of URIs of trusted origins)
A browser receiving content with this header MUST NOT display this content in any frame from a page of different origin than any of the listed origins. This allows deployment with multi-domain sites, as the webmaster can define a whitelist of origins that are allowed to frame the page. While this can expose the page to risks by the trusted origins, in some cases it may be necessary to use content from other domains or more than one origin (hostname).

2.2. Backus-Naur Form (BNF)

      Frame-Options = "Frame-Options" ":" "DENY"/ "SAMEORIGIN" / 
		              ("TRUSTED" ":" Origin-List)
	  Origin-List = 1*URI
	  

The RFC 822 [RFC0822] EBNF of the Frame-Options header is:




[TBD] Or should we use the ABNF (RFC 2234) alternatively or in addition?

2.3. Examples of Frame-Options Headers

3. Acknowledgements

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

4. IANA Considerations

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

4.1. Registration Template

PERMANENT MESSAGE HEADER FIELD REGISTRATION TEMPLATE:

Header field name: Frame-Option

Applicable protocol: http [RFC2616]

Status: Standard
      
Author/Change controller: IETF

Specification document(s): draft-gondrom-frame-options

Related information:
            

5. Security Considerations

The introduction of the http header FRAME-OPTIONS does improve the protection against Clickjacking, however it is not self-sufficient on its own but MUST be used in conjunction with other security measures like secure coding and Content Security Policy (CSP)

6. References

6.1. Normative References

6.2. Informative References

Appendix A. Description of a Clickjacking attack

More detailed explanation of a Clickjacking attack

Authors' Addresses