Preventing Time Synchronization in NTP's Broadcast Mode
This addresses a security vulnerability in NTP that could disrupt critical Internet services like DNS and routing, though it is incremental as it focuses on a specific mode.
The paper identifies a new attack that prevents clients in NTP's broadcast mode from synchronizing their clocks, demonstrating its effectiveness in real networks and revealing that several high-accuracy hosts are vulnerable.
Network Time Protocol (NTP) is used by millions of hosts in Internet today to synchronize their clocks. Clock synchronization is necessary for many network applications to function correctly. Unsynchronized clock may lead to failure of various core Internet services including DNS and RPKI based interdomain routing and opens path for more sophisticated attacks. In this paper, we describe a new attack which can prevent a client configured in NTP's 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 NTP broadcast mode is being used in the wild by several low stratum (highly accurate) hosts. We also suggest few countermeasures to mitigate the proposed attack.