Port Randomization in the Network Time Protocol Version 4
draft-gont-ntp-port-randomization-01

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Last updated 2019-05-20
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Network Time Protocol (ntp) Working Group                        F. Gont
Internet-Draft                                                   G. Gont
Obsoletes: rfc5905 (if approved)                            SI6 Networks
Intended status: Standards Track                            May 20, 2019
Expires: November 21, 2019

       Port Randomization in the Network Time Protocol Version 4
                  draft-gont-ntp-port-randomization-01

Abstract

   The Network Time Protocol can operate in several modes.  Some of
   these modes are based on the receipt of unsolicited packets, and
   therefore require the use of a service/well-known port as the local
   port number.  However, in the case of NTP modes where the use of a
   service/well-known port is not required, employing such well-known/
   service port unnecessarily increases the ability of attackers to
   perform blind/off-path attacks, since knowledge of such port number
   is typically required for such attacks.  This document formally
   updates RFC5905, recommending the use of port randomization for those
   modes where use of the NTP service port is not required.

Status of This Memo

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   Copyright (c) 2019 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
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   (https://trustee.ietf.org/license-info) in effect on the date of

Gont & Gont             Expires November 21, 2019               [Page 1]
Internet-Draft           NTP Port Randomization                 May 2019

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Update to RFC5905 . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Implementation Status . . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The Network Time Protocol (NTP) is one of the oldest Internet
   protocols, and currently specified in [RFC5905].  Since its its
   original implementation, standardization and deployment, a number of
   vulnerabilities have been found both in the NTP specification and in
   some of its implementations [NTP-VULN].  Some of these
   vulnerabilities allow for off-path/blind attacks, where an attacker
   can send forged packets to one or both NTP peers for achieving Denial
   of Service (DoS), time-shifts, and other undesirable outcomes.  Many
   of these attacks require the attacker to guess or know at least a
   target association, typically identified by the tuple {srcaddr,
   srcport, dstaddr, dstport, keyid}. Some of these parameters may be
   easily known or guessed.

   NTP can operate in several modes.  Some of these modes rely on the
   ability to receive unsolicited packets, and therefore require the use
   of a service/well-known port number.  However, for modes where the
   use of a service/well-known port is not required, employing such
   well-known/service port improves the ability of an attacker to
   perform blind/off-path attacks (since knowledge of such port number
   is typically required for such attacks).  A recent study [NIST-NTP]
   that analyzes the port numbers employed by NTP peers suggests that a
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