CVE-2015-7978 in ntp
Summary
by MITRE
NTP before 4.2.8p6 and 4.3.0 before 4.3.90 allows a remote attackers to cause a denial of service (stack exhaustion) via an ntpdc relist command, which triggers recursive traversal of the restriction list.
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Analysis
by VulDB Data Team • 05/17/2026
The vulnerability identified as CVE-2015-7978 represents a critical stack exhaustion flaw in the Network Time Protocol implementation that affects versions prior to 4.2.8p6 and 4.3.90. This vulnerability specifically targets the ntpdc utility's relist command functionality, which serves as a diagnostic tool for querying NTP daemon configuration and restriction lists. The flaw stems from inadequate input validation and recursive traversal logic that fails to properly limit the depth of nested restriction list processing. When a remote attacker crafts a malicious ntpdc relist command with specially constructed restriction list data, the NTP daemon enters an infinite recursive loop that consumes stack memory until system resources are exhausted, resulting in a complete denial of service condition that affects time synchronization services across affected systems.
The technical implementation of this vulnerability aligns with CWE-674, which describes "Uncontrolled Recursion" in software systems where recursive functions lack proper termination conditions or depth limits. The attack vector operates through the ntpdc protocol interface, which is designed for remote management and diagnostics of NTP daemon operations. When the relist command processes restriction lists containing circular references or deeply nested structures, the recursive traversal mechanism fails to maintain proper stack bounds checking. This recursive traversal pattern creates a stack exhaustion condition where each recursive call consumes additional stack space without proper bounds enforcement, eventually leading to stack overflow and daemon termination. The vulnerability demonstrates characteristics consistent with ATT&CK technique T1499.004, which involves network denial of service attacks through resource exhaustion, specifically targeting memory allocation patterns within network services.
The operational impact of CVE-2015-7978 extends beyond simple service disruption to compromise the reliability and availability of time synchronization infrastructure critical for numerous network operations. Organizations relying on NTP for time stamping, authentication protocols, and system coordination face potential cascading failures when affected NTP daemons become unavailable. The vulnerability affects systems where ntpdc is accessible to remote attackers, including enterprise networks, cloud environments, and internet-facing time servers. Network administrators may observe sudden service outages, failed authentication attempts, and disrupted time-based operations across affected infrastructure. The denial of service condition can persist until system administrators manually restart the NTP daemon or implement temporary network segmentation to block access to the vulnerable ntpdc interface. Recovery from this vulnerability requires immediate patching of NTP implementations to enforce proper recursion limits and stack depth validation.
Mitigation strategies for CVE-2015-7978 should prioritize immediate patch deployment to NTP versions 4.2.8p6 and 4.3.90 or later, which contain fixed recursion depth limits and enhanced input validation. Network segmentation and access control measures should be implemented to restrict remote access to the ntpdc interface, particularly on internet-facing systems. Organizations should also implement monitoring for unusual ntpdc command usage patterns and establish automated alerting for potential exploitation attempts. The NTP project recommends disabling the ntpdc utility on systems where it is not required for operational purposes, as this eliminates the attack surface entirely. Additionally, system administrators should verify that NTP daemon configurations properly limit the number of concurrent connections and implement proper resource limits to prevent stack exhaustion even if other vulnerabilities exist. Security teams should conduct vulnerability assessments to identify all systems running affected NTP versions and establish a remediation timeline to ensure complete network coverage against this specific denial of service attack vector.