NTP Symmetric Key Authentication Security Vulnerabilities Patched

NTP, the much maligned protocol abused in a number of high volume DDoS attacks a year ago, is suffering from newly patched vulnerabilities that could allow an attacker to send unauthenticated packets to a client that would be executed.

The Department of Homeland Security and CERT at the Software Engineering Institute at Carnegie Mellon University on Tuesday issued an advisory warning of the two vulnerabilities, which were patched in ntp-4.2 8p2.

The first vulnerability, CVE-2015-1798, affects ntp-4.2.5p99 to ntp-4.2.8p1 versions using symmetric key authentication. According to the advisory, packets sent without message authentication code (MAC) are accepted as though they had one.

“An attacker may be able to leverage this validation error to send packets that will be accepted by the client,” the advisory said.

The second flaw affects versions xntp3.3wy to version ntp-4.2.8p1 that use symmetric key authentication, and creates a denial of service condition when peering hosts receive packets where the timestamps don’t match.

“An attacker who periodically sends such packets to both hosts can prevent synchronization,” the advisory said.

NTP is a protocol used to synchronize time on computer clocks; considered a set-and-forget feature on networks. Hackers who specialize in distributed denial-of-service attacks found a way to exploit vulnerabilities in NTP to amplify DDoS attacks to, at the time, unprecedented levels.

Last February, traffic optimization company CloudFlare reported a NTP-based DDoS attack against one of its customers that peaked at 400 Gbps, topping the previous high of 300 Gbps against Spamhaus in March 2013.

“Remarkably, it is possible that the attacker used only a single server running on a network that allowed source IP address spoofing to initiate the requests,” CloudFlare CEO Matthew Prince told Threatpost at the time.

NTP-based DDoS attacks are a relatively simple way of spoofing IP addresses in order to disrupt websites or web-based services.

“NTP attacks are definitely on the rise. Because the amplification factor per misconfigured server can be 10x as large as a typical DNS amplification attack, they pose a significant risk,” Prince said.

Red Hat’s Miroslav Lichvar reported the issue in early March to NTP, which patched the vulnerabilities yesterday.