CVE-2016-2516 in ntp
Summary
by MITRE
NTP before 4.2.8p7 and 4.3.x before 4.3.92, when mode7 is enabled, allows remote attackers to cause a denial of service (ntpd abort) by using the same IP address multiple times in an unconfig directive.
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Analysis
by VulDB Data Team • 07/27/2022
The vulnerability identified as CVE-2016-2516 affects the Network Time Protocol implementation in ntpd versions prior to 4.2.8p7 and 4.3.x versions prior to 4.3.92. This issue specifically manifests when the mode7 protocol is enabled, which is a legacy feature designed for time synchronization between clients and servers. The flaw resides in how ntpd handles the unconfig directive when multiple instances of the same IP address are provided, creating a condition that leads to system instability and potential service disruption.
The technical exploitation of this vulnerability involves sending specially crafted packets containing the unconfig directive with repeated IP addresses to a vulnerable ntpd daemon. When the daemon processes these malformed requests, it triggers an abort condition that causes the ntpd process to terminate unexpectedly. This behavior represents a classic denial of service vulnerability that can be exploited remotely without requiring authentication or special privileges. The vulnerability is particularly concerning because it can be triggered through legitimate network traffic and does not require complex attack vectors or specific environmental conditions to be effective.
From an operational perspective, this vulnerability presents significant risk to network infrastructure that relies on NTP for time synchronization. The denial of service condition can disrupt time synchronization across entire networks, affecting critical systems that depend on accurate timekeeping for logging, authentication, and security event correlation. The impact extends beyond simple service disruption as time synchronization failures can cascade into broader network reliability issues, particularly in environments where precise timing is essential for coordinated operations. Organizations with multiple NTP servers or those operating in high-availability configurations may experience service degradation or complete outages when this vulnerability is exploited.
The vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and falls under ATT&CK technique T1499.001 for network denial of service attacks. The exploitation pattern demonstrates how legacy protocol features can introduce security weaknesses that persist across multiple versions of software implementations. Organizations should prioritize patching affected systems and consider disabling mode7 functionality when it is not required for operations. Additionally, implementing network monitoring to detect unusual patterns in NTP traffic and establishing redundant time synchronization sources can help mitigate the impact of potential exploitation attempts. The vulnerability serves as a reminder of the importance of maintaining current security patches and regularly reviewing protocol configurations to eliminate unnecessary features that may introduce attack surface vulnerabilities.