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 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 20, 2007. 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. Gerhards Expires January 20, 2007 [Page 1] Internet-Draft SSH transport mapping for SYSLOG July 2006 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 Gerhards Expires January 20, 2007 [Page 2] Internet-Draft SSH transport mapping for SYSLOG July 2006 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. Gerhards Expires January 20, 2007 [Page 3] Internet-Draft SSH transport mapping for SYSLOG July 2006 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 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 Gerhards Expires January 20, 2007 [Page 4] Internet-Draft SSH transport mapping for SYSLOG July 2006 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 . 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 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. Gerhards Expires January 20, 2007 [Page 5] Internet-Draft SSH transport mapping for SYSLOG July 2006 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: Gerhards Expires January 20, 2007 [Page 6] Internet-Draft SSH transport mapping for SYSLOG July 2006 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 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 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 Gerhards Expires January 20, 2007 [Page 7] Internet-Draft SSH transport mapping for SYSLOG July 2006 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. Gerhards Expires January 20, 2007 [Page 8] Internet-Draft SSH transport mapping for SYSLOG July 2006 Author's Address Rainer Gerhards Adiscon GmbH Mozartstrasse 21 Grossrinderfeld, BW 97950 Germany Email: rgerhards@adiscon.com Gerhards Expires January 20, 2007 [Page 9] Internet-Draft SSH transport mapping for SYSLOG July 2006 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Gerhards Expires January 20, 2007 [Page 10]