CVE-2015-7975 in ntp
Summary
by MITRE
The nextvar function in NTP before 4.2.8p6 and 4.3.x before 4.3.90 does not properly validate the length of its input, which allows an attacker to cause a denial of service (application crash).
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Analysis
by VulDB Data Team • 05/17/2026
The vulnerability identified as CVE-2015-7975 affects the Network Time Protocol implementation in versions prior to 4.2.8p6 and 4.3.x before 4.3.90. This issue resides within the nextvar function which is responsible for processing variable-length data structures in the NTP protocol. The flaw represents a classic buffer over-read condition where the function fails to adequately validate input length parameters before processing them. This type of vulnerability falls under the broader category of improper input validation as classified by CWE-20, which is a fundamental weakness in software design that allows malicious inputs to cause unexpected behavior. The NTP protocol serves as a critical infrastructure component for time synchronization across networked systems, making this vulnerability particularly concerning from a security operations perspective.
The technical exploitation of this vulnerability occurs when an attacker crafts malformed input data that exceeds the expected buffer boundaries within the nextvar function. When the function attempts to process this oversized input without proper length validation, it reads beyond allocated memory regions, leading to unpredictable application behavior and ultimately causing the NTP daemon to crash. This denial of service condition affects the availability of time synchronization services across affected systems, potentially disrupting critical network operations that depend on accurate timekeeping. The vulnerability demonstrates characteristics consistent with CWE-129, which addresses improper validation of array indices, as the function fails to validate that input data fits within expected bounds before processing.
From an operational standpoint, this vulnerability presents significant risk to organizations relying on NTP for time synchronization, particularly in environments where continuous availability is critical. The impact extends beyond individual system compromise to potentially affect entire network infrastructures that depend on synchronized timekeeping for security logging, authentication protocols, and distributed system coordination. Attackers can leverage this vulnerability to perform sustained denial of service attacks against NTP servers, causing cascading failures that may affect multiple dependent services and systems. The vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and represents a common attack vector in the context of infrastructure service disruption.
The recommended mitigation strategy involves immediate deployment of patched NTP versions, specifically 4.2.8p6 or later for the 4.2.x series and 4.3.90 or later for the 4.3.x series. Organizations should also implement network monitoring to detect unusual traffic patterns that may indicate exploitation attempts, and consider deploying intrusion detection systems that can identify malformed NTP packets. Additional defensive measures include implementing rate limiting on NTP traffic and ensuring that NTP servers are properly isolated within network security zones. Security teams should conduct comprehensive vulnerability assessments to identify all systems running affected NTP versions and prioritize patching based on the criticality of time synchronization services within their environments. The remediation process should follow established security patch management procedures to ensure consistent deployment across all affected infrastructure components while maintaining operational continuity.