Pierluigi Paganini January 04, 2014

Security researchers at Symantec have spotted a series of Network Time Protocol (NTP) reflection DDoS attacks during the Christmas Holidays.

DDoS attacks are very simple methods of offence that could cause serious problems to targeted systems, behind the word DDoS there are numerous techniques that could be exploited by attackers to reach their goals.

Last year principal security firms observed a significant increase of the DDoS attacks, the report issued by Arbor Networks on global DDoS attack trends for the first three-quarters of 2013 provides an interesting overview of Internet traffic patterns and threat evolution. The data show a constant growth in the number or attacks and related efficiency, the analysts observed a significant increase (32%) for malicious traffic, the IPv4 traffic reached  69Tbps of peak, up from 47Tbps in registered in  Q2.

In particular is has been observed an increase in the adoption of DDoS methodology known as Distributed Reflection Denial of Service attacks (DrDoS) that substantially exploits misconfigured DNS (Domain Name System) to launch powerful DDoS attacks. The abuse of DNS systems is just an option for the attacker, security researchers at Symantec have spotted a new insidious method to conduct DDoS attacks, cyber criminals started a series of Network Time Protocol (NTP) reflection DDoS attacks during the Christmas Holidays.

In the below graph it is possible to note that on December 16th were observed nearly 15000 IP addresses involved in the Network Time Protocol (NTP) reflection DDoS attack likely belonging to a botnet.

The Network Time Protocol (NTP) is a networking protocol widely used  for clock synchronization purpose between systems over packet-switched, variable-latency data networks.

Network Time Protocol (NTP) implementations exchange timestamps using the User Datagram Protocol (UDP) on port number 123.

“NTP is one of those set-it-and-forget-it protocols that is configured once and most network administrators don’t worry about it after that.  Unfortunately, that means it is also not a service that is upgraded often, leaving it vulnerable to these reflection attacks.”  states the Symantec post to highlight how much dangerous is to not consider the evolution of each service that is used by our systems.

Exactly as DNS Reflection attack, in the Network Time Protocol (NTP) reflection DDoS the hackers sends a small spoofed 8-byte UDP packets to the vulnerable NTP server that requests megabytes of data to be sent to the target IP Address.

CVE has already coded the Network Time Protocol vulnerability as CVE-2013-5211, the attackers exploit the monlist command for the offensives.

“Monlist is a remote command in older version of NTP that sends the requester a list of the last 600 hosts who have connected to that server.  For attackers the monlist query is a great reconnaissance tool.  For a localized NTP server it can help to build a network profile.  However, as a DDoS tool, it is even better because a small query can redirect megabytes worth of traffic” reports Symantec.

[root@server ~]# ntpdc -c monlist [hostname]

To protect Network Time Protocol server it is necessary to update it to NTP 4.2.7, a version that has excluded the support of ‘monlist’ query substituted by a new safe ‘mrunlist’ function which uses a nonce value ensuring that received IP address match the actual requester.

“If upgrading is not an option, you can start the NTP daemon with noquery enabled in the NTP conf file.  This will disable access to mode 6 and 7 query packetts (which includes monlist). “

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Pierluigi Paganini

(Security Affairs –  Network Time Protocol (NTP) reflection DDoS, Symantec)