NTP.org’s ntpd prior to version 4.2.8p9 contains multiple denial of service vulnerabilities.

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."

CWE-400: Uncontrolled Resource Consumption (‘Resource Exhaustion’) – CVE-2016-9310

According to NTP.org, "An exploitable configuration modification vulnerability exists in the control mode (mode 6) functionality of ntpd. If, against long-standing BCP recommendations, "restrict default noquery …" is not specified, a specially crafted control mode packet can set ntpd traps, providing information disclosure and DDoS amplification, and unset ntpd traps, disabling legitimate monitoring. A remote, unauthenticated, network attacker can trigger this vulnerability."

CWE-400: Uncontrolled Resource Consumption (‘Resource Exhaustion’) – CVE-2016-7427

According to NTP.org, "The broadcast mode of NTP is expected to only be used in a trusted network. If the broadcast network is accessible to an attacker, a potentially exploitable denial of service vulnerability in ntpd’s broadcast mode replay prevention functionality can be abused. An attacker with access to the NTP broadcast domain can periodically inject specially crafted broadcast mode NTP packets into the broadcast domain which, while being logged by ntpd, can cause ntpd to reject broadcast mode packets from legitimate NTP broadcast servers."

CWE-400: Uncontrolled Resource Consumption (‘Resource Exhaustion’) – CVE-2016-7428

According to NTP.org, "The broadcast mode of NTP is expected to only be used in a trusted network. If the broadcast network is accessible to an attacker, a potentially exploitable denial of service vulnerability in ntpd’s broadcast mode poll interval enforcement functionality can be abused. To limit abuse, ntpd restricts the rate at which each broadcast association will process incoming packets. ntpd will reject broadcast mode packets that arrive before the poll interval specified in the preceding broadcast packet expires. An attacker with access to the NTP broadcast domain can send specially crafted broadcast mode NTP packets to the broadcast domain which, while being logged by ntpd, will cause ntpd to reject broadcast mode packets from legitimate NTP broadcast servers."

CWE-410: Insufficient Resource Pool – CVE-2016-9312

According to NTP.org, "If a vulnerable instance of ntpd on Windows receives a crafted malicious packet that is "too big", ntpd will stop working."

CWE-20: Improper Input Validation – CVE-2016-7431

According to NTP.org, "Zero Origin timestamp problems were fixed by Bug 2945 in ntp-4.2.8p6. However, subsequent timestamp validation checks introduced a regression in the handling of some Zero origin timestamp checks."

CWE-20: Improper Input Validation – CVE-2016-7434

According to NTP.org, "If ntpd is configured to allow mrulist query requests from a server that sends a crafted malicious packet, ntpd will crash on receipt of that crafted malicious mrulist query packet."

CWE-605: Multiple Binds to the Same Port – CVE-2016-7429

According to NTP.org, "When ntpd receives a server response on a socket that corresponds to a different interface than was used for the request, the peer structure is updated to use the interface for new requests. If ntpd is running on a host with multiple interfaces in separate networks and the operating system doesn’t check source address in received packets (e.g. rp_filter on Linux is set to 0), an attacker that knows the address of the source can send a packet with spoofed source address which will cause ntpd to select wrong interface for the source and prevent it from sending new requests until the list of interfaces is refreshed, which happens on routing changes or every 5 minutes by default. If the attack is repeated often enough (once per second), ntpd will not be able to synchronize with the source."

CWE-410: Insufficient Resource Pool – CVE-2016-7426

According to NTP.org, "When ntpd is configured with rate limiting for all associations (restrict default limited in ntp.conf), the limits are applied also to responses received from its configured sources. An attacker who knows the sources (e.g., from an IPv4 refid in server response) and knows the system is (mis)configured in this way can periodically send packets with spoofed source address to keep the rate limiting activated and prevent ntpd from accepting valid responses from its sources."

CWE-682: Incorrect Calculation – CVE-2016-7433

According to NTP.org, "Bug 2085 described a condition where the root delay was included twice, causing the jitter value to be higher than expected. Due to a misinterpretation of a small-print variable in The Book, the fix for this problem was incorrect, resulting in a root distance that did not include the peer dispersion. The calculations and formulae have been reviewed and reconciled, and the code has been updated accordingly."

For more information, please see NTP.org’s security advisory.

The CVSS score below is based on CVE-2016-9312.

A remote unauthenticated attacker may be able to perform a denial of service on ntpd.

Implement BCP-38.

Use "restrict default noquery ..." in your ntp.conf file. Only allow mode 6 queries from trusted networks and hosts.

Apply an update

Upgrade to 4.2.8p9, or later, from the NTP Project Download Page or the NTP Public Services Project Download Page.

Monitor ntpd

Properly monitor your ntpd instances, and auto-restart ntpd (without -g) if it stops running.