CVE-2015-7977 in ntp
Summary
by MITRE
ntpd in NTP before 4.2.8p6 and 4.3.x before 4.3.90 allows remote attackers to cause a denial of service (NULL pointer dereference) via a ntpdc reslist command.
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Analysis
by VulDB Data Team • 05/17/2026
The vulnerability identified as CVE-2015-7977 affects the Network Time Protocol daemon (ntpd) in versions prior to 4.2.8p6 and 4.3.x prior to 4.3.90. This issue represents a critical denial of service weakness that can be exploited by remote attackers to crash the ntpd service through a specific command execution path. The vulnerability specifically manifests when processing the ntpdc reslist command, which is part of the NTP diagnostic and control interface designed for network time synchronization management.
The technical flaw underlying CVE-2015-7977 constitutes a NULL pointer dereference condition that occurs within the ntpd implementation when handling malformed or specially crafted input to the reslist command. This type of vulnerability falls under the Common Weakness Enumeration category CWE-476, which specifically addresses NULL pointer dereference scenarios where software attempts to access memory through a null reference. The vulnerability exists in the command processing logic of the ntpdc utility, which serves as the control interface for ntpd, allowing administrators to query and manage time synchronization parameters. When a remote attacker sends a malformed reslist command to a vulnerable ntpd instance, the daemon fails to properly validate input parameters before attempting to dereference a pointer that remains uninitialized or set to NULL.
The operational impact of this vulnerability extends beyond simple service disruption as it enables remote attackers to systematically crash time synchronization services across networked systems. This denial of service condition affects critical infrastructure components that rely on accurate timekeeping for security logging, authentication mechanisms, and timestamp-based operations. The vulnerability is particularly concerning because it does not require authentication or specific privileges to exploit, making it accessible to any remote entity capable of reaching the target system's NTP service port. Network time synchronization servers that are exposed to the internet or untrusted networks become prime targets for this attack vector, potentially leading to cascading failures in time-sensitive applications and services that depend on consistent time synchronization.
The exploitation of CVE-2015-7977 aligns with tactics described in the MITRE ATT&CK framework under the T1499 category for Network Denial of Service, where adversaries target network services to disrupt availability. This vulnerability can be leveraged in coordinated attacks against multiple time servers, potentially causing widespread disruption in systems that rely on NTP for operational continuity. Organizations using older NTP versions are particularly vulnerable as the patch for this issue was released in the 4.2.8p6 and 4.3.90 releases, making it essential for system administrators to implement immediate remediation measures. The vulnerability demonstrates the importance of proper input validation and defensive programming practices in network services, as the lack of proper bounds checking and null pointer validation created an exploitable condition that could be triggered remotely.
Mitigation strategies for CVE-2015-7977 primarily focus on upgrading to patched versions of the NTP software, specifically NTP 4.2.8p6 or later, and NTP 4.3.90 or later. System administrators should also implement network segmentation and access controls to limit exposure of NTP services to untrusted networks, while configuring firewall rules to restrict access to NTP ports. Additional defensive measures include monitoring for unusual command execution patterns and implementing intrusion detection systems that can identify potential exploitation attempts. The vulnerability highlights the necessity of maintaining current security patches and the importance of conducting regular vulnerability assessments to identify and remediate similar issues in network infrastructure components. Organizations should also consider implementing redundant time synchronization services to ensure continued availability during remediation activities and to minimize the impact of potential exploitation attempts.