misc/185371: NTPD vulnerable to being used for DDOS

[Brian Rak]

>Number:         185371
>Category:       misc
>Synopsis:       NTPD vulnerable to being used for DDOS
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Dec 31 17:30:00 UTC 2013
>Closed-Date:
>Last-Modified:
>Originator:     Brian Rak
>Release:        9.1.0
>Organization:
>Environment:
FreeBSD XXXX 9.1-RELEASE FreeBSD 9.1-RELEASE #0 r243825: Tue Dec  4 09:23:10 UTC 2012     root at farrell.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  amd64
>Description:
The FreeBSD default ntp.conf makes the NTP server vulnerable to being used for a DDOS attack.

Please see:
http://www.symantec.com/connect/blogs/hackers-spend-christmas-break-launching-large-scale-ntp-reflection-attacks

https://isc.sans.edu/diary/NTP+reflection+attack/17300

https://cert.litnet.lt/en/docs/ntp-distributed-reflection-dos-attacks

The issue is in this configuration file:
http://svnweb.freebsd.org/base/release/9.2.0/etc/ntp.conf?revision=255898&view=markup

All the restrict lines are commented out (for reasons I'm unsure of, the comments don't make any sense).


>How-To-Repeat:
To determine if a server is vulnerable:

ntpdc -c monlist SERVERIP

If you see a list of hosts, rather then 'timed out, nothing received', the machine can be exploited in this way.
>Fix:
You can replace all the existing (commented) restrict lines with the following:

restrict default kod limited nomodify notrap nopeer noquery
restrict -6 default kod limited nomodify notrap nopeer noquery
restrict 127.0.0.1
restrict -6 ::1

This configuration will allow the NTP daemon to function correctly both as a client and server, and prevent it from being abused in this way.

>Release-Note:
>Audit-Trail:
>Unformatted: