Arch Linux Security Advisory ASA-201606-4
========================================
Severity: High
Date    : 2016-06-04
CVE-ID  : CVE-2016-4953 CVE-2016-4954 CVE-2016-4955 CVE-2016-4956
          CVE-2016-4957 
Package : ntp
Type    : distributed denial of service amplification
Remote  : Yes
Link    : https://wiki.archlinux.org/title/CVE

Summary
======
The package ntp before version 4.2.8.p8-1 can be used to amplify distributed
denial of service (DDoS) attacks.

Resolution
=========
Upgrade to 4.2.8.p8-1.

# pacman -Syu "ntp>=4.2.8.p8-1"

The problem has been fixed upstream in version 4.2.8.p8.

Workaround
=========
Implement ingress and egress filtering through BCP38.

Description
==========
- CVE-2016-4953 (distributed denial of service amplification)

An attacker who knows the origin timestamp and can send a spoofed packet
containing a CRYPTO-NAK to an ephemeral peer target before any other
response is sent can demobilize that association.  
Credit to Miroslav Lichvar of Red Hat

- CVE-2016-4954 (distributed denial of service amplification)

An attacker who is able to spoof packets with correct origin timestamps from
enough servers before the expected response packets arrive at the target
machine can affect some peer variables and, for example, cause a false leap
indication to be set. Credit to Jakub Prokes of Red Hat

- CVE-2016-4955 (distributed denial of service amplification)

An attacker who is able to spoof a packet with a correct origin timestamp
before the expected response packet arrives at the target machine can send a
CRYPTO_NAK or a bad MAC and cause the association's peer variables to be
cleared. If this can be done often enough, it will prevent that association
from working. Credit to Miroslav Lichvar of Red Hat

- CVE-2016-4956 (distributed denial of service amplification)

The fix for NtpBug2978 does not cover broadcast associations, so broadcast
clients can be triggered to flip into interleave mode.  
Credit to Miroslav Lichvar of Red Hat

- CVE-2016-4957 (distributed denial of service amplification)

The fix for Sec 3007 in ntp-4.2.8p7 contained a bug that could cause ntpd to
crash. Credit to Nicolas Edet of Cisco

Impact
=====
A remote attacker can utilize unpatched or improperly filtered NTP servers
as participants in distributed denial of service attacks (DDoS).

References
=========
https://www.ntp.org/support/securitynotice/ntpbug3042/
https://access.redhat.com/security/cve/cve-2016-4956
https://www.ntp.org/support/securitynotice/ntpbug3043/
https://access.redhat.com/security/cve/cve-2016-4955
https://www.ntp.org/support/securitynotice/ntpbug3044/
https://access.redhat.com/security/cve/cve-2016-4954
https://www.ntp.org/support/securitynotice/ntpbug3045/
https://access.redhat.com/security/cve/cve-2016-4953
https://www.ntp.org/support/securitynotice/ntpbug3046/
https://access.redhat.com/security/cve/cve-2016-4957