CVE-2015-7704 in ntpd
Summary
by MITRE
The ntpd client in NTP 4.x before 4.2.8p4 and 4.3.x before 4.3.77 allows remote attackers to cause a denial of service via a number of crafted "KOD" messages.
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Analysis
by VulDB Data Team • 06/25/2022
The vulnerability identified as CVE-2015-7704 represents a significant denial of service weakness in the Network Time Protocol implementation within ntpd clients. This flaw affects NTP versions 4.x prior to 4.2.8p4 and 4.3.x prior to 4.3.77, creating a critical risk for network infrastructure that relies on time synchronization services. The vulnerability specifically targets the handling of KOD (Kiss of Death) messages, which are legitimate NTP control messages used to signal when a server should stop responding to client requests. However, this particular vulnerability allows attackers to exploit the message processing logic to trigger system resource exhaustion and subsequent service disruption.
The technical implementation of this vulnerability stems from insufficient input validation and resource management within the ntpd client's KOD message processing routine. When an attacker sends multiple crafted KOD messages to a vulnerable NTP server, the system fails to properly handle the excessive message volume and processing requirements. This leads to resource exhaustion, typically manifesting as memory allocation failures or process starvation. The flaw operates at the protocol level where the ntpd daemon does not adequately limit the rate or volume of KOD messages it processes, allowing malicious actors to flood the system with carefully constructed messages that consume system resources without proper bounds checking. This behavior aligns with CWE-400, which catalogs improper resource management vulnerabilities that can lead to denial of service conditions.
The operational impact of CVE-2015-7704 extends beyond simple service disruption to potentially compromise broader network infrastructure reliability. Organizations relying on NTP for time synchronization across critical systems face the risk of cascading failures when vulnerable ntpd instances are targeted. The vulnerability can be exploited remotely without authentication requirements, making it particularly dangerous in environments where network exposure is high. Attackers can leverage this weakness to disrupt time synchronization services that are fundamental to many security protocols, logging systems, and network operations. The attack vector is particularly concerning because it can be executed from any location with network access to the vulnerable NTP server, and the effects can persist until the system is manually restarted or the vulnerable software is patched. This vulnerability directly maps to ATT&CK technique T1499.001, which covers network denial of service attacks targeting time synchronization services.
Mitigation strategies for CVE-2015-7704 primarily focus on immediate software updates to versions 4.2.8p4 or 4.3.77, which contain the necessary patches to properly handle KOD message processing. Network administrators should implement rate limiting and message filtering mechanisms at network boundaries to reduce the impact of potential attacks. The patch addresses the core issue by introducing proper bounds checking and resource management for KOD message processing, ensuring that the system can handle unexpected message volumes without exhausting critical resources. Additionally, organizations should consider implementing network segmentation and access controls to limit exposure of NTP servers to untrusted networks. Monitoring systems should be configured to detect unusual KOD message patterns that could indicate exploitation attempts, providing early warning capabilities for potential attacks. The vulnerability demonstrates the importance of maintaining current security patches and highlights the need for proper input validation in protocol implementations that handle external data streams.