Port Randomization in the Network Time Protocol Version 4
draft-ietf-ntp-port-randomization-05
Network Time Protocol (ntp) Working Group F. Gont
Internet-Draft G. Gont
Updates: rfc5905 (if approved) SI6 Networks
Intended status: Standards Track M. Lichvar
Expires: January 27, 2021 Red Hat
July 26, 2020
Port Randomization in the Network Time Protocol Version 4
draft-ietf-ntp-port-randomization-05
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. 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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This Internet-Draft will expire on January 27, 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Considerations About Port Randomization in NTP . . . . . . . 3
3.1. Mitigation Against Off-path Attacks . . . . . . . . . . . 3
3.2. Effects on Path Selection . . . . . . . . . . . . . . . . 4
3.3. Filtering of NTP traffic . . . . . . . . . . . . . . . . 4
3.4. Effect on NAT devices . . . . . . . . . . . . . . . . . . 5
3.5. Relation to Other Mitigations for Off-Path Attacks . . . 5
4. Update to RFC5905 . . . . . . . . . . . . . . . . . . . . . . 5
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The Network Time Protocol (NTP) is one of the oldest Internet
protocols, and currently specified in [RFC5905]. Since 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, or other undesirable outcomes. Many
of these attacks require the attacker to guess or know at least a
target NTP 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 of nodes to receive unsolicited packets, and therefore
require the use of a service/well-known port number (123). However,
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