This is a purely informative rendering of an RFC that includes verified errata. This rendering may not be used as a reference.
The following 'Verified' errata have been incorporated in this document:
EID 3267, EID 3455
Internet Engineering Task Force (IETF) B. Trammell
Request for Comments: 6546 ETH Zurich
Obsoletes: 6046 April 2012
Category: Standards Track
ISSN: 2070-1721
Transport of Real-time Inter-network Defense (RID) Messages
over HTTP/TLS
Abstract
The Incident Object Description Exchange Format (IODEF) defines a
common XML format for document exchange, and Real-time Inter-network
Defense (RID) defines extensions to IODEF intended for the
cooperative handling of security incidents within consortia of
network operators and enterprises. This document specifies an
application-layer protocol for RID based upon the passing of RID
messages over HTTP/TLS.
Status of This Memo
This is an Internet Standards Track document.
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). Further information on
Internet Standards is available in 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/rfc6546.
Copyright Notice
Copyright (c) 2012 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
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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.
1. Introduction
The Incident Object Description Exchange Format (IODEF) [RFC5070]
describes an XML document format for the purpose of exchanging data
between Computer Security Incident Response Teams (CSIRTs) or those
responsible for security incident handling for service providers
(SPs). The defined document format provides a simple way for CSIRTs
to exchange data in a way which can be easily parsed.
IODEF defines a message format, not a protocol, as the sharing of
messages is assumed to be out of scope in order to allow CSIRTs to
exchange and store messages in a way most suited to their established
incident-handling processes. However, Real-time Inter-network
Defense (RID) [RFC6545] does require a specification of a protocol to
ensure interoperability among members in a RID consortium. This
document specifies the transport of RID messages within HTTP
[RFC2616] Request and Response messages over TLS [RFC5246] (herein,
HTTP/TLS). Note that any IODEF message may also be transported using
this mechanism, by sending it as a RID Report message.
1.1. Changes from RFC 6046
This document contains the following changes with respect to its
predecessor [RFC6046]:
o The status of the document is Standards Track.
o The document is updated to refer to the updated RID specification,
[RFC6545], where appropriate.
o Language regarding the use of HTTP/1.1 and TCP ports for RID
transport is clarified.
o The RID-Callback-Token entity header field is added to allow
matching of RID replies during callback, independent of the
content of the underlying RID message.
o The minimum required version of TLS is upgraded to 1.1, and the
minimum recommended version to 1.2.
o Language regarding PKI for RID over HTTPS is clarified, and
updated to refer to [RFC6125].
This document obsoletes [RFC6046] and moves it to Historic status.
2. Terminology and Normative Sections
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 [RFC2119].
RID systems participating in a consortium are required to fully
implement the protocol in Section 3 in order to interoperate within
the consortium; the remainder of this document is informative and
provides helpful background or explanatory information.
3. Transmission of RID Messages over HTTP/TLS
EID 3267 (Verified) is as follows:Section: 3
Original Text:
In paragraph 4 of section 3, fourth sentence:
As RID messages MUST be
sent using the POST method, the GET and HEAD methods have no
particular meaning on a RID system; a RID system SHOULD answer
'GET /' or 'HEAD /' with 204 No Content.
Corrected Text:
Consistent with RFC 2616 section 10.4.6, a RID system MUST answer
any HTTP request to Request-URI of '/' which uses an HTTP method
other than 'POST' by producing an HTTP response with a status code
of 405 Method Not Allowed. The RID system HTTP response MUST also
include an Allow header indicating that only the 'POST' method is
supported.
Notes:
There has been a brief discussion of this errata on the MILE list, with the first message in the thread having been posted on June 5, 2012.
The corrected text that I have suggested above has been written as narrowly as possible, and remains consistent with the original functionality described in 6546.
Lacking support for 'GET' means that there is no way to verify if a RID endpoint is active, other than by doing a real request, i.e. a Report, or Query, etc. Thus, one might also consider supporting HEAD, e.g. for RID testing purposes, though that option has not been discussed yet. Note, however, that supporting HEAD potentially raises further issues since according to RFC 2616 the response headers to a HEAD request SHOULD be consistent with a GET, which is specifically not supported.
This section specifies the details of the transport of RID messages
[RFC6545] over HTTP/TLS. In this arrangement, each RID server is
both an HTTP/TLS server and an HTTP/TLS client. When a RID message
is sent, the sending RID system connects to the receiving RID system
and sends the message, optionally receiving a message in reply. Each
RID system MUST be prepared to accept HTTP/TLS connections from any
RID peer with which it communicates, in order to support callback for
delayed replies (see below).
BCP 56 [RFC3205] contains a number of important considerations when
using HTTP for application protocols. These include the size of the
payload for the application, whether the application will use a web
browser, whether the protocol should be defined on a port other than
80, and if the security provided through HTTP/TLS suits the needs of
the new application.
It is acknowledged within the scope of these concerns that HTTP/TLS
is not ideally suited for RID transport, as the former is a client-
server protocol and the latter a message-exchange protocol; however,
the ease of implementation of RID systems over HTTP/TLS outweighs
these concerns. Consistent with BCP 56, RID systems listen for TCP
connections on port 4590 (see Section 5). Every RID system
participating in a consortium SHOULD listen for HTTP/TLS connections
on the assigned port. RID systems MAY be configurable to listen on
ports other than the well-known port; this configuration is out of
scope for this specification. RID systems SHOULD NOT use TCP port
443 (the standard port for HTTP over TLS) for RID messages in order
to avoid confusing standard HTTP/TLS servers for RID systems.
RID systems MUST implement all REQUIRED functionality for HTTP/1.1
[RFC2616]. All RID messages sent in HTTP Requests MUST be sent using
the POST method with a Request-URI of '/'. As RID documents are XML,
the RID media type is 'text/xml'; i.e., the 'Content-type' Request
and Response headers MUST be 'text/xml'. As RID messages MUST be
sent using the POST method, the GET and HEAD methods have no
particular meaning on a RID system; a RID system SHOULD answer
'GET /' or 'HEAD /' with 204 No Content. Other Request-URIs are
reserved for future use; any access to Request-URIs other than '/' by
any method on a RID system SHOULD return the appropriate HTTP error
(404 Not Found).
Since the content of RID messages is essentially declarative, a RID
system interrupted during transport MAY simply repeat the
transaction; the sending of a RID message is idempotent.
As the queries and replies in a RID message exchange may be
significantly separated in time, RID over HTTP/TLS supports a
callback mechanism. In this mechanism, the receiving RID system MAY
return a 202 Accepted response, called a RID callback, instead of a
RID message. The RID callback MUST contain a zero-length entity body
and a 'RID-Callback-Token' entity header field, itself containing a
unique token generated by the receiving RID system.
The RID-Callback-Token is an opaque, whitespace-free string of up to
255 printable ASCII characters that MUST uniquely identify the
callback among all callbacks from the receiving RID system to the
sending RID system. Due to the amount of time that may be required
to generate a RID Result or Report response, there is no upper bound
on the time period for this uniqueness requirement. The RID-
Callback-Token in ABNF [RFC5234] form is shown below:
callback-token = 1*255(VCHAR)
When performing RID callback, a responding system MUST connect to the
host at the network-layer address from which the original request was
sent; there is no mechanism in RID for redirected callback. This
callback SHOULD use TCP port 4590 unless configured to use a
different port.
While a RID system SHOULD return the reply in an HTTP Response if it
is available immediately or within a generally accepted HTTP client
timeout (about thirty seconds), this is not mandatory, and as such
RID systems MUST be prepared for a query to be met with a 202
Accepted, an empty Response body, a connection termination, and a
callback. Note that all RID messages require a response from the
receiving RID system, so a sending RID system can expect either an
immediate response or a callback.
Table 1 lists the allowable RID message types in an HTTP Response for
a given RID message type in the Request. A RID system MUST be
prepared to handle an HTTP Response of the given type(s) when sending
the corresponding HTTP Request. A RID system MUST NOT send an HTTP
Response containing any RID message other than the one corresponding
to the one sent in the HTTP Request.
+----------------------+----------+--------+-------------------+
| Request RID type | Callback | Result | Response RID type |
+----------------------+----------+--------+-------------------+
| InvestigationRequest | | 200 | Acknowledgement |
| InvestigationRequest | | 200 | Result |
| InvestigationRequest | | 200 | Report |
| InvestigationRequest | | 202 | [empty] |
| TraceRequest | | 200 | Acknowledgement |
| TraceRequest | | 200 | Result |
| TraceRequest | | 200 | Report |
| TraceRequest | | 202 | [empty] |
| Query | | 200 | Acknowledgement |
| Query | | 200 | Report |
| Query | | 202 | [empty] |
| Acknowledgement | X | 200 | [empty] |
| Result | X | 200 | [empty] |
| Report | | 200 | Acknowledgement |
| Report | | 200 | [empty] |
| Report | X | 200 | [empty] |
+----------------------+----------+--------+-------------------+
Table 1
The use of stable DNS names to address RID systems is RECOMMENDED; in
addition to facilitating connection to RID systems within a
consortium, these are to be used as reference identifiers for a RID
system's peers. For security purposes, RID systems SHOULD NOT return
3xx Redirection response codes, and SHOULD NOT follow any 3xx
Redirection. The protocol provides no in-band method for handling a
change of address of a RID system.
If a RID system receives an improper HTTP Request, it MUST return
an appropriate 4xx Client Error result code to the requesting RID
system.
If a RID system cannot process a RID message
EID 3455 (Verified) is as follows:Section: 3
Original Text:
If a RID system receives an improper RID message in an HTTP Request,
it MUST return an appropriate 4xx Client Error result code to the
requesting RID system.
Corrected Text:
If a RID system receives an improper HTTP Request, it MUST return
an appropriate 4xx Client Error result code to the requesting RID
system.
Notes:
There has been some discussion of this issue on the MILE mailing list. Another possible option for the corrected text is to say nothing at all. That is, by changing the specification to focus on an improper HTTP request, rather than an improper RID message, the corrected text is simply a restatement of existing HTTP behavior. (Either way, this still does constitute a technical change since we would no longer be requiring the 400 status code when the error is with the *RID* content). On this technical point, we had consensus on the MILE mailing list: we SHOULD NOT require an HTTP 4xx status code when there is an error with the RID content itself (as opposed to the HTTP layer). HTTP 4xx status is reserved for errors occurring in the HTTP protocol layer. Errors in the RID content will be reported via the RID Acknowledgement message type, with appropriate choices for the RequestStatus element, and Justification attribute.
received in an HTTP Request due to an error on its own side, it MUST
return an appropriate 5xx Server Error result code to the requesting
RID system.
Note that HTTP provides no mechanism for signaling to a server that a
response body is not a valid RID message. If a RID system receives
an improper RID message in an HTTP Response, or cannot process a RID
message received in an HTTP Response due to an error on its own side,
it MUST log the error and present it to the RID system administrator
for handling; the error logging format is an implementation detail
and is considered out of scope for this specification.
RID systems MUST support and SHOULD use HTTP/1.1 persistent
connections as described in [RFC2616]. RID systems MUST support
chunked transfer encoding on the HTTP server side to allow the
implementation of clients that do not need to pre-calculate message
sizes before constructing HTTP headers.
RID systems MUST use TLS version 1.1 [RFC4346] or higher for
confidentiality, identification, and authentication, when sending RID
messages over HTTPS. HTTPS is specified in Section 2 of [RFC2818].
RID systems MUST use mutual authentication; that is, both RID systems
acting as HTTPS clients and RID systems acting as HTTPS servers MUST
be identified by an X.509 certificate [RFC5280]. Mutual
authentication requires full path validation on each certificate, as
defined in [RFC5280].
The TLS session MUST use non-NULL ciphersuites for authentication,
integrity, and confidentiality. Sessions MAY be renegotiated within
these constraints.
All RID systems SHOULD be identified by a certificate containing
DNS-ID identifier as in Section 6.4 of [RFC6125]; the inclusion of
Common Names (CN-IDs) in certificates identifying RID systems is NOT
RECOMMENDED. RID systems MUST verify the reference identifiers of
their peers against those stored in the certificates presented using
one of the methods in the following paragraph. Wildcards MUST NOT
appear in the DNS-ID or CN-ID of a certificate identifying a RID
system.
RID systems MUST support the verification of certificates against an
explicit whitelist of peer certificates. RID systems SHOULD support
the verification of reference identifiers by matching the DNS-ID or
CN-ID with a reverse DNS lookup of the connecting RID peer; this
support SHOULD allow the lookup to be cached and/or done in advance
in order to ensure verifiability during instability or compromise of
DNS itself.
Additional general information on the use of PKI with RID systems is
detailed in Section 9.3 of [RFC6545].
RID systems MUST support TLS version 1.1 and SHOULD support TLS
version 1.2 [RFC5246]; RID systems MUST NOT request, offer, or use
any version of SSL, or any version of TLS prior to 1.1, due to known
security vulnerabilities in prior versions of the protocol; see
Appendix E of [RFC5246] for more information.
4. Security Considerations
In addition to the final paragraphs in Section 3 on the use of TLS to
secure RID message transport, all security considerations of related
documents apply, especially the Incident Object Description Exchange
Format (IODEF) [RFC5070] and Real-time Inter-network Defense (RID)
[RFC6545]. The protocol described herein is built on the foundation
of those documents; the security considerations contained therein are
incorporated by reference.
5. IANA Considerations
Consistent with BCP 56 [RFC3205], since RID over HTTP/TLS is a
substantially new service, and should be controlled at the consortium
member network's border differently than HTTP/TLS, it requires a new
port number. IANA has assigned port 4590/tcp to RID with service
name "RID over HTTP/TLS".
6. Acknowledgements
The author would like to thank David Black for the review, and
Kathleen Moriarty for work on earlier revisions of this
specification. This work was partially supported by the European
Union Seventh Framework Program under grant agreement 257315
(DEMONS).
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC5070] Danyliw, R., Meijer, J., and Y. Demchenko, "The Incident
Object Description Exchange Format", RFC 5070,
December 2007.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011.
[RFC6545] Moriarty, K., "Real-time Inter-network Defense (RID)",
RFC 6545, April 2012.
7.2. Informative References
[RFC3205] Moore, K., "On the use of HTTP as a Substrate", BCP 56,
RFC 3205, February 2002.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC6046] Moriarty, K. and B. Trammell, "Transport of Real-time
Inter-network Defense (RID) Messages", RFC 6046,
November 2010.
Author's Address
Brian Trammell
Swiss Federal Institute of Technology Zurich
Gloriastrasse 35
8092 Zurich
Switzerland
Phone: +41 44 632 70 13
EMail: trammell@tik.ee.ethz.ch