Internet DRAFT - draft-gerhards-syslog-transport-ssh

draft-gerhards-syslog-transport-ssh







SYSLOG Working Group                                         R. Gerhards
Internet-Draft                                              Adiscon GmbH
Expires: January 20, 2007                                  July 19, 2006


                    SSH transport mapping for SYSLOG
               draft-gerhards-syslog-transport-ssh-00.txt

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document describes a method for invoking and running the SYSLOG
   protocol within a Secure Shell (SSH) session as an SSH subsystem.










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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Security Requirements for SYSLOG . . . . . . . . . . . . . . .  3
   3.  Conventions Used in This Document  . . . . . . . . . . . . . .  4
   4.  Starting SYSLOG over SSH . . . . . . . . . . . . . . . . . . .  4
   5.  Using SYSLOG over SSH  . . . . . . . . . . . . . . . . . . . .  5
     5.1.  framing  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   6.  Exiting the SYSLOG Subsystem . . . . . . . . . . . . . . . . .  5
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  6
   8.  Authors  . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  7
   11. Notes to the RFC Editor  . . . . . . . . . . . . . . . . . . .  7
   12. Normative  . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .  9
   Intellectual Property and Copyright Statements . . . . . . . . . . 10


































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1.  Introduction

   The SYSLOG protocol [9] is a text-based protocol used to convey event
   information.  SYSLOG is defined to be session-layer and transport
   independent, allowing mappings to be defined for multiple session-
   layer or transport protocols.  This document defines how SYSLOG can
   be used within a Secure Shell (SSH) session, using the SSH connection
   protocol RFC4254 [8] over the SSH transport protocol RFC4253 [7].
   This mapping will allow SYSLOG to be executed from a secure shell
   session by a user or application.  Throughout this document, the
   terms "client" and "server" are used to refer to the two ends of the
   SSH transport connection.  The client actively opens the SSH
   connection, and the server passively listens for the incoming SSH
   connection.  The terms "sender" and "receiver" are used to refer to
   the two ends of the SYSLOG protocol session and are consistent with
   the definitions in SYSLOG-protocol.  When SYSLOG is run over SSH
   using the mapping defined in this document, the client is always the
   sender, and the server is always the receiver.  This document
   describes a layered architecture for SYSLOG.  The goal of this
   architecture is to separate message content from message transport
   while enabling easy extensibility for each layer.


2.  Security Requirements for SYSLOG

   SYSLOG messages may pass several hops to arrive at the intended
   receiver.  Some intermediary networks may not be trusted by the
   sender or the receiver or both because the network is in a different
   security domain or at a different security level from the receiver or
   sender.  Another security concern is that the sender or receiver
   itself is in an insecure network.

   There are several threats to be addressed for SYSLOG security.  The
   primary threats are:
   o  Masquerade.  An unauthorized sender may send messages to a
      legitimate receiver, or an unauthorized receiver tries to deceive
      a legitimate sender into sending SYSLOG messages to it.
   o  Modification.  An attacker between the sender and receiver may
      modify an in-transit SYSLOG message from the sender and then
      forward the message to receiver.  Such modification may make the
      receiver misunderstands the message or causes the receiver to
      behave in undesirable ways.
   o  Disclosure.  An unauthorized entity may examine the content of the
      SYSLOG messages, gaining unauthorized access to the information.
      Some data in SYSLOG messages is sensitive and may be useful to an
      attacker, such as the password of an authorized administrator or
      user.




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   The secondary threat is:
   o  Message stream modification.  An attacker may delete a SYSLOG
      message from a series of messages, replay a message or alter the
      delivery sequence.  SYSLOG protocol itself is not based on message
      order, but an event in a SYSLOG message may relate semantically to
      events in other messages, so message ordering may be important to
      understanding a sequence of events.

   The following threats are deemed to be of lesser importance for
   SYSLOG, and are not addressed in this document:
   o  Denial of Service
   o  Traffic Analysis


3.  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 RFC 2119 [1].


4.  Starting SYSLOG over SSH

   To run SYSLOG over SSH, the client will first establish an SSH
   transport connection using the SSH transport protocol, and the client
   and server will exchange keys for message integrity and encryption.
   The client will then invoke the "ssh-userauth" service to
   authenticate the user, as described in the SSH authentication
   protocol RFC4252 [6].  Once the user has been successfully
   authenticated, the client will invoke the "ssh-connection" service,
   also known as the SSH connection protocol.

   After the ssh-connection service is established, the client will open
   a channel of type "session", which will result in an SSH session.

   Once the SSH session has been established, the user (or application)
   will invoke SYSLOG as an SSH subsystem called "syslog".  Subsystem
   support is a feature of SSH version 2 (SSHv2) and is not included in
   SSHv1.  Running SYSLOG as a SSH subsystem avoids the need for the
   script to recognize shell prompts or skip over extraneous
   information, such as a system message that is sent at shell start-up.
   However, if a subsystem cannot be used, it should be possible for a
   client to skip over any system messages that are sent at shell
   start-up by searching for a SYSLOG <hello> element.  Note that this
   may not avoid problems if system messages are recieved later in the
   session.

   In order to allow SYSLOG traffic to be easily identified and filtered



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   by firewalls and other network devices, SYSLOG servers MUST default
   to providing access to the "syslog" SSH subsystem only when the SSH
   session is established using the IANA-assigned TCP port <TBD>.
   Servers SHOULD be configurable to allow access to the syslog SSH
   subsystem over other ports.

   A user (or application), could use the following command line to
   invoke SYSLOG as an SSH subsystem on the IANA-assigned port:

   [user@client]$ ssh -s server.example.org -p <TBD> syslog

   Note that the -s option causes the command ("syslog") to be invoked
   as an SSH subsystem.


5.  Using SYSLOG over SSH

   A SYSLOG over SSH session consists of the client sending a continous
   stream of syslog frames to the receiver.  The receiver does not
   acknowledge frames.

5.1.  framing

   The SYSLOG frame has the following ABNF [2] definition:

     SYSLOG-FRAME = HEADER SP SYSLOG-MSG TRAILER
     HEADER = ENTITY SP FRAME-LEN
     ENTITY = "MSG"
     FRAME-LEN = NONZERO-DIGIT 0*DIGIT
     SP = %d32
     DIGIT = %d48 / NONZERO-DIGIT
     NONZERO-DIGIT = %d49-57
     TRAILER = CRLF

   Figure 1

   SYSLOG-MSG is defined in RFCXXXX [9].

   [This text needs to be edited once the specific framing has been
   selected.  This eventually happens in a separate document.]


6.  Exiting the SYSLOG Subsystem

   Exiting SYSLOG is accomplished using the "CLOSE" operation verb on
   the frame stream.  If the server receivers the "CLOSE" operation, it
   will return an "ACK" and terminate the connetion.




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   The server MAY decide to terminate a session at its discretion.  In
   this case, the underlying SSH connection is terminated.  No
   notification other than the SSH error occurs to the server.

   [This text needs to be edited once the specific framing has been
   selected.  This eventually happens in a separate document.]


7.  Security Considerations

   SYSLOG is used to convey potentially sensitive information, so the
   ability to access this protocol should be limited to users and
   systems that are authorized to view this information.

   The identity of the server MUST be verified and authenticated by the
   client according to local policy before password-based authentication
   data or any configuration or state data is sent to or received from
   the server.  The identity of the client MUST also be verified and
   authenticated by the server according to local policy to ensure that
   the incoming client request is legitimate before any configuration or
   state data is sent to or received from the client.  Neither side
   should establish a syslog over SSH connection with an unknown,
   unexpected or incorrect identity on the opposite side.

   SYSLOG messages may include sensitive information, such as usernames
   or security keys.  So, SYSLOG should only be used over communications
   channels that provide strong encryption for data privacy.  This
   document defines a SYSLOG over SSH mapping which provides for support
   of strong encryption and authentication.

   This document requires that servers default to allowing access to the
   "syslog" SSH subsystem only when using a specific TCP port assigned
   by IANA for this purpose.  This will allow SYSLOG over SSH traffic to
   be easily identified and filtered by firewalls and other network
   nodes.  However, it will also allow SYSLOG over SSH traffic to be
   more easily identified by attackers.

   This document also recommends that servers be configurable to allow
   access to the "syslog" SSH subsystem over other ports.  Use of that
   configuration option without corresponding changes to firewall or
   network device configuration may unintentionally result in the
   ability for nodes outside of the firewall or other administrative
   boundary to gain access to "syslog" SSH subsystem.


8.  Authors

   The author of this draft is:



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         Rainer Gerhards
         Email: rgerhards@adiscon.com

         Phone: +49-9349-92880
         Fax: +49-9349-928820

         Adiscon GmbH
         Mozartstrasse 21
         97950 Grossrinderfeld
         Germany


9.  IANA Considerations

   IANA is requested to assign a TCP port number which will be the
   default port for SYSLOG over SSH sessions as defined in this
   document.

   IANA has assigned port <TBD> for this purpose.

   IANA is also requested to assign "syslog" as an SSH Service Name as
   defined in RFC 4250 [5] as follows:

           Service Name                  Reference
           -------------                 ---------
           syslog                        [This Document]


10.  Acknowledgments

   This document was written using the xml2rfc tool described in RFC2629
   [4].

   The authors wish to thank Chris Lonvick, Anton Okmianski, David
   Harrington, Tom Petch, and all other people who commented on various
   versions of this proposal.


11.  Notes to the RFC Editor

   These are notes to the RFC editor.  Please delete this section after
   the notes have been followed.

   Please replace the instances of <TBD> the port number assigned by
   IANA.

   This ID is submitted along with draft-ietf-syslog-protocol.  When a
   RFC number is determined for draft-ietf-syslog-protocol, replace XXXX



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   in RFCXXXX with the proper RFC number.

12.  Normative

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
        Specifications: ABNF", RFC 2234, November 1997.

   [3]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
        Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.

   [4]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
        June 1999.

   [5]  Lehtinen, S. and C. Lonvick, "The Secure Shell (SSH) Protocol
        Assigned Numbers", RFC 4250, January 2006.

   [6]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
        Authentication Protocol", RFC 4252, January 2006.

   [7]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Transport
        Layer Protocol", RFC 4253, January 2006.

   [8]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Connection
        Protocol", RFC 4254, January 2006.

   [9]  Gerhards, R., "The syslog Protocol",
        draft-ietf-syslog-protocol-17 (work in progress), June 2006.





















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Author's Address

   Rainer Gerhards
   Adiscon GmbH
   Mozartstrasse 21
   Grossrinderfeld, BW  97950
   Germany

   Email: rgerhards@adiscon.com










































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