CVE-2016-9311 NTP DoS Exploit Released, update your Windows server asap

The flaw was discovered by the security researcher Magnus Stubman, it can be exploited to cause the crash of the NTP daemon and triggers a denial-of-service (DoS) condition on Windows systems.

A patch was developed and sent to Stubman on 29th September. The researcher acknowledged the fix a couple of days later and then publicly disclosed the flaw.

“The vulnerability allows unauthenticated users to crash ntpd with a single malformed UDP packet, which causes a null pointer dereference,” Stubman wrote in an advisory published Monday.

“CWE-476: NULL Pointer Dereference – CVE-2016-9311

“According to NTP.org, “ntpd does not enable trap service by default. If trap service has been explicitly enabled, an attacker can send a specially crafted packet to cause a null pointer dereference that will crash ntpd, resulting in a denial of service. Affects Windows only.” reads the Vulnerability Note VU#633847 issued by the CERT at the Software Engineering Institute at Carnegie Mellon University.

Stubman released a PoC exploit that can cause the crash of the NTP daemon and triggers a denial-of-service (DoS) condition on Windows systems. This means that theoretically everyone could crash a server with just a single specifically crafted packet.

“NTP users are strongly urged to take immediate action to ensure that their NTP daemons are not susceptible to being used in distributed denial-of-service (DDoS) attacks. Please also take this opportunity to defeat denial-of-service attacks by implementing Ingress and Egress filtering through BCP38. ntp-4.2.8p9 was released on 21 November 2016 and addresses 1 high- (Windows only), 2 medium-, 2 medium-/low-, and 5 low-severity security issues, 28 bugfixes, and contains other improvements over 4.2.8p8.

Please see the NTP Security Notice for vulnerability and mitigation details.” reads the security notice. 

Giving a close look at the NTP security notice we can find another critical issue, a trap-crash vulnerability reported by the expert Matthew Van Gundy from Cisco.

“If trap service has been explicitly enabled, an attacker can send a specially crafted packet to cause a null pointer dereference that will crash ntpd, resulting in a denial of service,” reads the advisory.

The CERT at the Software Engineering Institute at Carnegie Mellon University has also listed some vendors that could be affected by the bugs.

Administrators urge to patch their NTP implementations as soon as possible due to the availability of the PoC exploit code.

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Pierluigi Paganini

(Security Affairs – NTP, CVE-2016-9311)