CVE-2016-7428 in ntpd
Summary
by MITRE
ntpd in NTP before 4.2.8p9 allows remote attackers to cause a denial of service (reject broadcast mode packets) via the poll interval in a broadcast packet.
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Analysis
by VulDB Data Team • 05/13/2026
The vulnerability identified as CVE-2016-7428 affects the Network Time Protocol daemon ntpd in versions prior to 4.2.8p9, representing a significant denial of service weakness that impacts network time synchronization services. This flaw specifically targets the broadcast mode packet handling mechanism within the NTP implementation, creating a scenario where remote attackers can exploit malformed poll interval values in broadcast packets to disrupt service availability. The vulnerability resides in the protocol's packet validation logic, where insufficient input sanitization allows malicious actors to craft specially formatted broadcast messages that trigger unexpected behavior in the ntpd process.
The technical exploitation of this vulnerability occurs through the manipulation of the poll interval field within NTP broadcast packets, which serves as a timing parameter that determines how frequently clients should poll for time updates. When ntpd receives a broadcast packet with an invalid or maliciously crafted poll interval value, the daemon fails to properly validate this parameter before processing the packet, leading to a rejection of the broadcast mode packet and subsequent service disruption. This behavior creates a denial of service condition where legitimate time synchronization requests are blocked, effectively preventing systems from maintaining accurate time coordination with the network.
From an operational perspective, this vulnerability poses substantial risk to network infrastructure relying on NTP for time synchronization, as it can be exploited by remote unauthenticated attackers to disrupt critical time services without requiring elevated privileges. The impact extends beyond simple service interruption to potentially affect time-sensitive applications, security systems, and network operations that depend on synchronized time stamps for log correlation, authentication mechanisms, and coordinated system operations. Organizations with extensive NTP deployments may experience cascading failures as time synchronization issues propagate through interconnected systems, particularly in environments where precise timing is essential for operational continuity.
The vulnerability aligns with CWE-129, which addresses improper validation of input ranges, and demonstrates characteristics consistent with attack patterns documented in the MITRE ATT&CK framework under the T1499 category for network denial of service. Organizations should implement immediate mitigations including upgrading to NTP version 4.2.8p9 or later, which includes proper input validation for poll interval values in broadcast mode packets. Additional defensive measures may include implementing network segmentation to limit broadcast packet access, deploying intrusion detection systems to monitor for suspicious NTP traffic patterns, and configuring access controls to restrict broadcast mode packet reception to trusted sources only. The remediation process should also involve thorough testing of updated NTP configurations to ensure compatibility with existing network time synchronization requirements while maintaining security posture against similar vulnerabilities.