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Keywords: IMAP4, internet message access protocol, client, server
Network Working Group T. Showalter
Request for Comments: 2971 Mirapoint, Inc.
Category: Standards Track October 2000
IMAP4 ID extension
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
The ID extension to the Internet Message Access Protocol - Version
4rev1 (IMAP4rev1) protocol allows the server and client to exchange
identification information on their implementation in order to make
bug reports and usage statistics more complete.
1. Introduction
The IMAP4rev1 protocol described in [IMAP4rev1] provides a method for
accessing remote mail stores, but it provides no facility to
advertise what program a client or server uses to provide service.
This makes it difficult for implementors to get complete bug reports
from users, as it is frequently difficult to know what client or
server is in use.
Additionally, some sites may wish to assemble usage statistics based
on what clients are used, but in an an environment where users are
permitted to obtain and maintain their own clients this is difficult
to accomplish.
The ID command provides a facility to advertise information on what
programs are being used along with contact information (should bugs
ever occur).
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RFC 2971 IMAP4 ID extension October 2000
2. Conventions Used in this Document
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 [KEYWORDS].
The conventions used in this document are the same as specified in
[IMAP4rev1]. In examples, "C:" and "S:" indicate lines sent by the
client and server respectively. Line breaks have been inserted for
readability.
3. Specification
The sole purpose of the ID extension is to enable clients and servers
to exchange information on their implementations for the purposes of
statistical analysis and problem determination.
This information is be submitted to a server by any client wishing to
provide information for statistical purposes, provided the server
advertises its willingness to take the information with the atom "ID"
included in the list of capabilities returned by the CAPABILITY
command.
Implementations MUST NOT make operational changes based on the data
sent as part of the ID command or response. The ID command is for
human consumption only, and is not to be used in improving the
performance of clients or servers.
This includes, but is not limited to, the following:
Servers MUST NOT attempt to work around client bugs by using
information from the ID command. Clients MUST NOT attempt to work
around server bugs based on the ID response.
Servers MUST NOT provide features to a client or otherwise
optimize for a particular client by using information from the ID
command. Clients MUST NOT provide features to a server or
otherwise optimize for a particular server based on the ID
response.
Servers MUST NOT deny access to or refuse service for a client
based on information from the ID command. Clients MUST NOT refuse
to operate or limit their operation with a server based on the ID
response.
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RFC 2971 IMAP4 ID extension October 2000
Rationale: It is imperative that this extension not supplant IMAP's
CAPABILITY mechanism with a ad-hoc approach where implementations
guess each other's features based on who they claim to be.
Implementations MUST NOT send false information in an ID command.
Implementations MAY send less information than they have available or
no information at all. Such behavior may be useful to preserve user
privacy. See Security Considerations, section 7.
3.1. ID Command
Arguments: client parameter list or NIL
Responses: OPTIONAL untagged response: ID
Result: OK identification information accepted
BAD command unknown or arguments invalid
Implementation identification information is sent by the client with
the ID command.
This command is valid in any state.
The information sent is in the form of a list of field/value pairs.
Fields are permitted to be any IMAP4 string, and values are permitted
to be any IMAP4 string or NIL. A value of NIL indicates that the
client can not or will not specify this information. The client may
also send NIL instead of the list, indicating that it wants to send
no information, but would still accept a server response.
The available fields are defined in section 3.3.
Example: C: a023 ID ("name" "sodr" "version" "19.34" "vendor"
"Pink Floyd Music Limited")
S: * ID NIL
S: a023 OK ID completed
3.2. ID Response
Contents: server parameter list
In response to an ID command issued by the client, the server replies
with a tagged response containing information on its implementation.
The format is the same as the client list.
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RFC 2971 IMAP4 ID extension October 2000
Example: C: a042 ID NIL
S: * ID ("name" "Cyrus" "version" "1.5" "os" "sunos"
"os-version" "5.5" "support-url"
"mailto:cyrus-bugs+@andrew.cmu.edu")
S: a042 OK ID command completed
A server MUST send a tagged ID response to an ID command. However, a
server MAY send NIL in place of the list.
3.3. Defined Field Values
Any string may be sent as a field, but the following are defined to
describe certain values that might be sent. Implementations are free
to send none, any, or all of these. Strings are not case-sensitive.
Field strings MUST NOT be longer than 30 octets. Value strings MUST
NOT be longer than 1024 octets. Implementations MUST NOT send more
than 30 field-value pairs.
name Name of the program
version Version number of the program
os Name of the operating system
os-version Version of the operating system
vendor Vendor of the client/server
support-url URL to contact for support
address Postal address of contact/vendor
date Date program was released, specified as a date-time
in IMAP4rev1
command Command used to start the program
arguments Arguments supplied on the command line, if any
if any
environment Description of environment, i.e., UNIX environment
variables or Windows registry settings
Implementations MUST NOT use contact information to submit automatic
bug reports. Implementations may include information from an ID
response in a report automatically prepared, but are prohibited from
sending the report without user authorization.
It is preferable to find the name and version of the underlying
operating system at runtime in cases where this is possible.
Information sent via an ID response may violate user privacy. See
Security Considerations, section 7.
Implementations MUST NOT send the same field name more than once.
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RFC 2971 IMAP4 ID extension October 2000
4. Formal Syntax
This syntax is intended to augment the grammar specified in
[IMAP4rev1] in order to provide for the ID command. This
specification uses the augmented Backus-Naur Form (BNF) notation as
used in [IMAP4rev1].
command_any ::= "CAPABILITY" / "LOGOUT" / "NOOP" / x_command / id
;; adds id command to command_any in [IMAP4rev1]
id ::= "ID" SPACE id_params_list
id_response ::= "ID" SPACE id_params_list
id_params_list ::= "(" #(string SPACE nstring) ")" / nil
;; list of field value pairs
response_data ::= "*" SPACE (resp_cond_state / resp_cond_bye /
mailbox_data / message_data / capability_data / id_response)
5. Use of the ID extension with Firewalls and Other Intermediaries
There exist proxies, firewalls, and other intermediary systems that
can intercept an IMAP session and make changes to the data exchanged
in the session. Such intermediaries are not anticipated by the IMAP4
protocol design and are not within the scope of the IMAP4 standard.
However, in order for the ID command to be useful in the presence of
such intermediaries, those intermediaries need to take special note
of the ID command and response. In particular, if an intermediary
changes any part of the IMAP session it must also change the ID
command to advertise its presence.
A firewall MAY act to block transmission of specific information
fields in the ID command and response that it believes reveal
information that could expose a security vulnerability. However, a
firewall SHOULD NOT disable the extension, when present, entirely,
and SHOULD NOT unconditionally remove either the client or server
list.
Finally, it should be noted that a firewall, when handling a
CAPABILITY response, MUST NOT allow the names of extensions to be
returned to the client that the firewall has no knowledge of.
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RFC 2971 IMAP4 ID extension October 2000
6. References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[IMAP4rev1] Crispin, M., "Internet Message Access Protocol - Version
4rev1", RFC 2060, October 1996.
[RFC-822] Crocker, D., "Standard for the Format of ARPA Internet
Text Messages", STD 11, RFC 822, August 1982.
7. Security Considerations
This extension has the danger of violating the privacy of users if
misused. Clients and servers should notify users that they implement
and enable the ID command.
It is highly desirable that implementations provide a method of
disabling ID support, perhaps by not sending ID at all, or by sending
NIL as the argument to the ID command or response.
Implementors must exercise extreme care in adding fields sent as part
of an ID command or response. Some fields, including a processor ID
number, Ethernet address, or other unique (or mostly unique)
identifier allow tracking of users in ways that violate user privacy
expectations.
Having implementation information of a given client or server may
make it easier for an attacker to gain unauthorized access due to
security holes.
Since this command includes arbitrary data and does not require the
user to authenticate, server implementations are cautioned to guard
against an attacker sending arbitrary garbage data in order to fill
up the ID log. In particular, if a server naively logs each ID
command to disk without inspecting it, an attacker can simply fire up
thousands of connections and send a few kilobytes of random data.
Servers have to guard against this. Methods include truncating
abnormally large responses; collating responses by storing only a
single copy, then keeping a counter of the number of times that
response has been seen; keeping only particularly interesting parts
of responses; and only logging responses of users who actually log
in.
Security is affected by firewalls which modify the IMAP protocol
stream; see section 5, Use of the ID Extension with Firewalls and
Other Intermediaries, for more information.
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RFC 2971 IMAP4 ID extension October 2000
8. Author's Address
Tim Showalter
Mirapoint, Inc.
909 Hermosa Ct.
Sunnyvale, CA 94095
EMail: tjs@mirapoint.com
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RFC 2971 IMAP4 ID extension October 2000
9. Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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