Preventing time synchronization in NTP broadcast mode

Abstract

Network Time Protocol (NTP) is used by millions of hosts on the Internet today to synchronize their clocks. The clock synchronization is necessary for many network applications to function correctly. An unsynchronized clock may lead to the failure of various core Internet services including DNS and RPKI based interdomain routing and opens the path for more sophisticated attacks. In this paper, we describe a new attack that can prevent a client configured in NTP broadcast mode from synchronizing its clock with the server. We test the attack in real networks and show that it is effective in both authenticated and unauthenticated broadcast/multicast modes of NTP. We also perform experiments to measure the overall attack surface by scanning the entire IPv4 address space and show that the NTP broadcast mode is being used in the wild by several low stratum (highly accurate) hosts. We also suggest a few countermeasures to mitigate the proposed attack. © 2020 Elsevier Ltd