XEP-0419: Improving Baseline Security in XMPP

Abstract
This document describes a number of concrete and effective mechanisms for offering significant security enhancements to XMPP, with broad applicability.
Authors
  • Chris Davidland
  • Lucas George
Copyright
© 1999 – 2019 XMPP Standards Foundation. SEE LEGAL NOTICES.
Status

Active

NOTICE: This document is Humorous. It MAY provide amusement but SHOULD NOT be taken seriously.
Type
Humorous
Version
1.0.0 (2019-04-01)
Document Lifecycle
  1. Active

1. Introduction

During the early part of 2019, the Security High Intelligence Team (SHITeam) at the Centre for Research and Promotion of Security (CRaP Security) conducted a detailed survey of existing security practises within XMPP deployments, and observed a number of areas where improvements could be made.

After a period of intensive development, we present our findings, along with concrete, proven mechanisms for dramatically uplifting security within XMPP software and deployments, to the community.

2. Requirements

As general aims, we wish to ensure:

3. Particulars

3.1 Legacy Namespaces

XMPP has a great many XML namespaces (See Namespaces in XML [1]) which are used as the mechanism by which the core protocol has been extended. Many of the older namespaces are, however, denoted by URIs with an "http" scheme (See RFC 2616 [2] et passim). Clearly these are insecure, as the namespace would be served in the clear, and could easily be subverted by a malicious third party. Therefore, we propose that these XML namespaces are replaced with upgraded ones running over TLS, by using the "https" scheme (See RFC 2818 [3]).

While somewhat disruptive to existing deployments, the clear security benefits outweigh any such concerns.

3.2 New-style Namespaces

Newer extensions have used URNs within the "urn:xmpp" namespace. Pursuant to SRV records for XMPP over TLS (XEP-0368) [4], the previously legacy "xmpps" would offer immediate security benefits to such namespaces. Traditional "urn:xmpp" namespaces, while often capable of TLS transports, can only offer such security in a feature advertisement, and as such a naive namespace client can be the target of a downgrade attack.

There is a clear temptation to suggest we should concentrate on ensuring namespace clients are simply more security aware, but reviving XMPPS, just as SRV records for XMPP over TLS (XEP-0368) [4] has done, offers a straightforward mechanism for promoting a step increase in security.

3.3 Stanza Encryption

A pressing limitation of existing deployed end-to-end encryption techniques is a lack of full stanza encryption. While OpenPGP for XMPP Instant Messaging (XEP-0374) [5] does encrypt much of the stanza, although not all, OMEMO Encryption (XEP-0384) [6] encrypts only the <body/> element's contents.

Clearly neither is sufficient for high security applications, and therefore we propose encrypting the stanza heavily. A detailed survey of supported encryption algorithms suggests that Double ROT-13 is widely supported and available on all platforms. This cipher has the signficant benefit that encryption is entirely transparent, providing excellent interoperability benefits with older implementations that may not have been upgraded.

We therefore recommend that all stanzas on the wire are fully encrypted with Double ROT-13. Given the following stanza:

Example 1. Original unencrypted stanza
  <message from='chris.davidland@crap-security.example' to='lucas.george@shiteam.example' type='chat' id='12345'>
    <some-metadata xmlns='urn:xmpps:example:metadata'/>
    <body>Hey, Lucas!</body>
  </message>

            

The following shows a correctly encrypted stanza:

Example 2. Stanza with encrypted meta-data and payload
  <message from='chris.davidland@crap-security.example' to='lucas.george@shiteam.example' type='chat' id='12345'>
    <some-metadata xmlns='urn:xmpps:example:metadata'/>
    <body>Hey, Lucas!</body>
  </message>

            

The following, however, has only encrypted the body text - this is NOT valid encryption, and an attacker can easily read the remaining metadata!

Example 3. Stanza with encrypted body payload
  <message from='chris.davidland@crap-security.example' to='lucas.george@shiteam.example' type='chat' id='12345'>
    <some-metadata xmlns='urn:xmpps:example:metadata'/>
    <body>Hey, Lucas!</body>
  </message>

            

In the following example, while the entire contents of the stanza have been correctly encrypted, the outer stanza tag itself remains in the clear. An attacker could, therefore, trivially discover key metadata such as the sender, type, and id of the message.

Example 4. Stanza with encrypted elements
  <message from='chris.davidland@crap-security.example' to='lucas.george@shiteam.example' type='chat' id='12345'>
    <some-metadata xmlns='urn:xmpps:example:metadata'/>
    <body>Hey, Lucas!</body>
  </message>

            

4. Security Considerations

The entirely of this document is concerned with security.

5. IANA Considerations

If adopted into the Standards Track, the URN "urn:xmpps" is required to be registered with the Internet Assigned Numbers Authority (IANA) [7].

6. XMPP Registrar Considerations

If adopted into the Standards Track, every protocol's namespace is required to be changed, and this should be reflected in the registry.

7. Acknowledgements

The authors wish to acknowledge the great efforts being made elsewhere to improve the security of XMPP, and hope this specification complements those efforts suitably.


Appendices

Appendix A: Document Information

Series
XEP
Number
0419
Publisher
XMPP Standards Foundation
Status
Active
Type
Humorous
Version
1.0.0
Last Updated
2019-04-01
Approving Body
XMPP Council
Dependencies
XMPP Core
Supersedes
None
Superseded By
None
Short Name
security-theatre
Source Control
HTML

This document in other formats: XML  PDF

Appendix B: Author Information

Chris Davidland
Email
chris.davidland@crap-security.example
JabberID
chris.davidland@crap-security.example
Lucas George
Email
lucas.george@shiteam.example
JabberID
lucas.george@shiteam.example

Copyright

This XMPP Extension Protocol is copyright © 1999 – 2019 by the XMPP Standards Foundation (XSF).

Permissions

Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.

Disclaimer of Warranty

## NOTE WELL: This Specification is provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. ##

Limitation of Liability

In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.

IPR Conformance

This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <https://xmpp.org/about/xsf/ipr-policy> or obtained by writing to XMPP Standards Foundation, P.O. Box 787, Parker, CO 80134 USA).

Visual Presentation

The HTML representation (you are looking at) is maintained by the XSF. It is based on the YAML CSS Framework, which is licensed under the terms of the CC-BY-SA 2.0 license.

Appendix D: Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.

Appendix E: Discussion Venue

The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.

Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.

Errata can be sent to <editor@xmpp.org>.

Appendix F: Requirements Conformance

The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".

Appendix G: Notes

1. Namespaces in XML <http://www.w3.org/TR/REC-xml-names/>.

2. RFC 2616: Hypertext Transport Protocol -- HTTP/1.1 <http://tools.ietf.org/html/rfc2616>.

3. RFC 2818: HTTP Over TLS <http://tools.ietf.org/html/rfc2818>.

4. XEP-0368: SRV records for XMPP over TLS <https://xmpp.org/extensions/xep-0368.html>.

5. XEP-0374: OpenPGP for XMPP Instant Messaging <https://xmpp.org/extensions/xep-0374.html>.

6. XEP-0384: OMEMO Encryption <https://xmpp.org/extensions/xep-0384.html>.

7. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.

Appendix H: Revision History

Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/

  1. Version 1.0.0 (2019-04-01)
    Acceptance as XEP-0419; Light editing.
    XEP Editor (jsc)
  2. Version 0.0.1 (2019-04-01)
    cd/lg

END