Network Working Group Y. Weiss
Internet-Draft Shopify
Intended status: Informational 20 March 2025
Expires: 21 September 2025
HttpOnly cookie prefix
draft-httponlyprefix-weiss-http-00
Abstract
This draft introduces the __HttpOnly and __HostHttpOnly cookie name
prefixes that ensure the cookie was set with an HttpOnly attribute.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at
https://yoavweiss.github.io/httponly_prefix/draft-httponlyprefix-
weiss-http.html. Status information for this document may be found
at https://datatracker.ietf.org/doc/draft-httponlyprefix-weiss-http/.
Source for this draft and an issue tracker can be found at
https://github.com/yoavweiss/httponly_prefix.
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Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions and Definitions . . . . . . . . . . . . . . . 3
2. Server Requirements . . . . . . . . . . . . . . . . . . . . . 3
2.1. Cookie Name Prefixes . . . . . . . . . . . . . . . . . . 3
2.1.1. The "__HttpOnly-" prefix . . . . . . . . . . . . . . 3
2.1.2. The "__HostHttpOnly-" prefix . . . . . . . . . . . . 3
3. User Agent Requirements . . . . . . . . . . . . . . . . . . . 4
3.1. Cookie Name Prefixes . . . . . . . . . . . . . . . . . . 4
3.1.1. Storage Model . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Normative References . . . . . . . . . . . . . . . . . . . . 5
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
There are cases where it's important to distinguish on the server
side between cookies [COOKIES] that were set by the server and ones
that were set by the client.
One such case is cookies that are normally _always_ set by the
server, unless some unexpected code (an XSS exploit, a malicious
extension, a commit from a confused developer, etc.) happens to set
them on the client.
This draft add a signal that would enable servers to make such a
distinction.
More specifically, it defines the __HttpOnly and __HostHttpOnly
prefixes, that make sure that a cookie is not set on the client side
using script.
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1.1. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Server Requirements
These requirements apply to cookies set in Set-Cookie response
headers by the server, as well as ones received in a Cookie request
header from the client.
2.1. Cookie Name Prefixes
2.1.1. The "__HttpOnly-" prefix
2.1.1.1. Cookie creation
If a server creates a cookie whose name begins with a case-sensitive
match for the string __HttpOnly-, then all the following MUST be
true:
1. The Set-Cookie HTTP header MUST include the Secure attribute.
2. The Set-Cookie HTTP header MUST include the HttpOnly attribute.
2.1.1.2. Cookie processing
If a server processes a cookie received in a Cookie request header
whose name begins with a case-sensitive match for the string
__HttpOnly-, this indicates that *all* the following are true:
1. The cookie was originally created using a Set-Cookie HTTP header
sent from this server.
2. The Set-Cookie HTTP header included the Secure attribute.
3. The Set-Cookie HTTP header included the HttpOnly attribute.
2.1.2. The "__HostHttpOnly-" prefix
2.1.2.1. Cookie creation
If a server uses a Set-Cookie HTTP header to create a cookie whose
name begins with a case-sensitive match for the string
__HostHttpOnly-, then all the following MUST be true:
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1. The Set-Cookie HTTP header MUST include the Secure attribute.
2. The Set-Cookie HTTP header MUST include the HttpOnly attribute.
3. The Set-Cookie HTTP header MUST include the Path attribute with a
value of /.
4. The Set-Cookie HTTP header MUST NOT include the Domain attribute.
2.1.2.2. Cookie processing
If a server processes a cookie received in a Cookie request header
whose name begins with a case-sensitive match for the string
__HostHttpOnly-, this indicates that *all* the following are true:
1. The cookie was originally created using a Set-Cookie HTTP header
sent from this server
2. The Set-Cookie HTTP header included the Secure attribute.
3. The Set-Cookie HTTP header included the HttpOnly attribute.
4. The Set-Cookie HTTP header included the Path attribute with a
value of /.
5. The Set-Cookie HTTP header did not include the Domain attribute.
3. User Agent Requirements
These requirements apply to cookies received in a Set-Cookie response
header from the server.
3.1. Cookie Name Prefixes
User agents' requirements for cookie name prefixes differ slightly
from servers', as UAs MUST match the prefix string case-
insensitively.
3.1.1. Storage Model
Add the following steps after step 21 of section 5.7 in [COOKIES].
1. If the cookie-name begins with a case-insensitive match for the
string "__HttpOnly-",
1. Abort these steps and ignore the cookie entirely unless all
the following conditions are true:
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1. The cookie's secure-only-flag is true.
2. The cookie's http-only-flag is true.
3. The cookie-attribute-list contains an attribute with an
attribute-name of "Path", and the cookie's path is "/".
2. If the cookie-name begins with a case-insensitive match for the
string "__HostHttpOnly-",
1. Abort these steps and ignore the cookie entirely unless all
the following conditions are true:
1. The cookie's secure-only-flag is true.
2. The cookie's http-only-flag is true.
3. The cookie's host-only-flag is true.
4. The cookie-attribute-list contains an attribute with an
attribute-name of "Path", and the cookie's path is "/".
5. The cookie-attribute-list does not contain an attribute
with an attribute-name of "Domain".
4. Security Considerations
There are no particular security considerations. These new prefixes
will only limit the ability of non-compliant cookies to be set. They
do not open up new capabilities for server to set cookies where they
previously could not.
5. IANA Considerations
This document has no IANA actions.
6. Normative References
[COOKIES] "Cookies HTTP State Management Mechanism", February 2025,
<https://datatracker.ietf.org/doc/draft-ietf-httpbis-
rfc6265bis/>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
Acknowledgments
Thanks to Rory Hewitt for his contributions to this draft. TODO
acknowledge.
Author's Address
Yoav Weiss
Shopify
Email: yoav@yoav.ws
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