Bug 1703341 (CVE-2019-11331)

Summary:	CVE-2019-11331 ntp: Using port 123 for modes where a fixed port number is not required facilitates off-path attacks.
Product:	[Other] Security Response	Reporter:	Marian Rehak <mrehak>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED WONTFIX	QA Contact:
Severity:	low	Docs Contact:
Priority:	low
Version:	unspecified	CC:	akjain, linville, mlichvar, yozone
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2019-06-10 10:54:46 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	1703342, 1705488
Bug Blocks:	1703344

Description Marian Rehak 2019-04-26 07:26:06 UTC

Network Time Protocol (NTP), as specified in RFC 5905, uses port 123 even for modes where a fixed port number is not required, which makes it easier for remote attackers to conduct off-path attacks.

Comment 1 Marian Rehak 2019-04-26 07:26:16 UTC

Created ntp tracking bugs for this issue:

Affects: fedora-all [bug 1703342]

Comment 7 Stefan Cornelius 2019-05-02 12:01:10 UTC

This is a weakness in the protocol.

Comment 19 Doran Moppert 2020-02-14 00:54:52 UTC

Mitigation:

On Red Hat Enterprise Linux 6 and later, switching from ntp to chrony is recommended. Among other design improvements, chrony uses a randomised source port by default.

If using ntp, the source port can be randomised by iptables masquerading rules, effectively mitigating this vulnerability:

    iptables -t nat -I POSTROUTING -p udp -m udp --sport 123 -j MASQUERADE --to-ports 60000-61000