CVE-2016-7429 in ntpd
Summary
by MITRE
NTP before 4.2.8p9 changes the peer structure to the interface it receives the response from a source, which allows remote attackers to cause a denial of service (prevent communication with a source) by sending a response for a source to an interface the source does not use.
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Analysis
by VulDB Data Team • 05/13/2026
The vulnerability identified as CVE-2016-7429 affects the Network Time Protocol implementation in versions prior to 4.2.8p9, representing a significant flaw in how NTP handles peer structure modifications during response processing. This vulnerability falls under the category of denial of service attacks and demonstrates a critical weakness in the protocol's ability to validate and manage network communication paths. The issue stems from the NTP daemon's improper handling of peer structures when processing responses from network sources, creating a scenario where malicious actors can manipulate the system's communication behavior through carefully crafted network packets.
The technical flaw occurs when NTP receives a response from a network source and incorrectly modifies the peer structure to reference an interface that differs from the one originally used for communication. This misconfiguration allows attackers to effectively redirect or block communication with legitimate time sources by exploiting the protocol's trust in response routing information. The vulnerability specifically targets the NTP daemon's internal state management mechanisms, where the peer structure is updated without proper validation of the interface consistency. This behavior creates a pathway for attackers to manipulate the daemon's understanding of network topology and communication paths, fundamentally undermining the protocol's reliability and security.
The operational impact of this vulnerability extends beyond simple service disruption to encompass potential compromise of time synchronization across critical network infrastructure. When exploited, the vulnerability can cause legitimate time sources to become unreachable or unusable, leading to cascading effects throughout networked systems that depend on accurate time synchronization for security operations, logging, and protocol coordination. The denial of service condition affects not just individual systems but can propagate through network hierarchies, particularly impacting time servers and critical infrastructure components that rely on NTP for maintaining synchronized operations. This vulnerability is particularly concerning in environments where time synchronization is crucial for security protocols, such as authentication systems, intrusion detection systems, and distributed application coordination.
Mitigation strategies for CVE-2016-7429 primarily focus on updating NTP implementations to versions 4.2.8p9 or later, which contain patches addressing the peer structure handling flaw. Network administrators should implement comprehensive monitoring of NTP traffic to detect anomalous behavior patterns that might indicate exploitation attempts. The vulnerability aligns with attack patterns documented in the ATT&CK framework under defense evasion and privilege escalation techniques, as it can be used to disrupt critical services and potentially gain further access to compromised systems. Organizations should also consider implementing network segmentation and access controls to limit exposure to potential attackers, while following industry best practices outlined in standards such as those provided by the National Institute of Standards and Technology for time synchronization security. The CWE database categorizes this issue under CWE-284, which deals with improper access control in network protocols, highlighting the fundamental security weakness in the NTP implementation's interface validation mechanisms.