CVE-2016-7434 in ntpd
Summary
by MITRE
The read_mru_list function in NTP before 4.2.8p9 allows remote attackers to cause a denial of service (crash) via a crafted mrulist query.
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Analysis
by VulDB Data Team • 05/13/2026
The vulnerability identified as CVE-2016-7434 affects the Network Time Protocol implementation in versions prior to 4.2.8p9, specifically within the read_mru_list function. This flaw represents a denial of service vulnerability that can be exploited by remote attackers to crash the NTP daemon through manipulation of mrulist queries. The issue stems from inadequate input validation and memory management within the function responsible for processing most recently used list queries, creating a condition where malformed data can trigger unexpected behavior in the time synchronization service.
The technical root cause of this vulnerability lies in the improper handling of memory references within the read_mru_list function, which processes queries related to the most recently used hosts list. When a remote attacker crafts a malicious mrulist query, the function fails to properly validate the input data structure, leading to potential memory corruption or access violations. This vulnerability falls under CWE-125, which describes out-of-bounds read conditions, and CWE-787, which covers out-of-bounds write operations. The flaw enables attackers to exploit memory management issues in the NTP implementation, potentially causing the daemon to crash and disrupting time synchronization services across affected networks.
The operational impact of CVE-2016-7434 extends beyond simple service disruption, as NTP servers form critical infrastructure components for network time synchronization and security operations. When exploited, this vulnerability can cause cascading effects throughout enterprise networks where NTP services are relied upon for timestamping, log correlation, authentication protocols, and security event monitoring. The attack vector requires minimal privileges and can be executed remotely, making it particularly dangerous for systems that are exposed to untrusted networks. Organizations running vulnerable NTP versions face potential service degradation, security monitoring gaps, and possible compromise of time-sensitive operations that depend on accurate timekeeping.
Mitigation strategies for this vulnerability center on immediate software updates to NTP versions 4.2.8p9 and later, which contain patches addressing the memory handling issues in the read_mru_list function. Network administrators should also implement access controls to limit query access to trusted sources, deploy intrusion detection systems to monitor for suspicious mrulist query patterns, and consider implementing network segmentation to reduce the attack surface. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, which covers network denial of service, and T1566.002, involving spearphishing via social media. Organizations should also review their NTP configuration practices and implement monitoring for unusual query patterns that could indicate exploitation attempts, ensuring comprehensive protection against this and similar memory-related vulnerabilities in time synchronization services.