CVE-2015-7850 in ntpd
Summary
by MITRE
ntpd in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows remote authenticated users to cause a denial of service (infinite loop or crash) by pointing the key file at the log file.
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Analysis
by VulDB Data Team • 06/24/2022
The vulnerability described in CVE-2015-7850 affects the Network Time Protocol daemon (ntpd) in versions prior to 4.2.8p4 and 4.3.77, representing a significant security flaw that enables authenticated remote attackers to disrupt network time synchronization services. This issue stems from improper handling of configuration file references where attackers can manipulate key file pointers to reference log files, creating a dangerous circular dependency that leads to system instability.
The technical flaw resides in how ntpd processes key file references within its configuration system, specifically when the key file path is set to point toward a log file location. When ntpd attempts to read or process the key file, it creates an infinite loop scenario where the system continuously attempts to update the log file while simultaneously processing the key file reference, resulting in either an infinite loop that consumes system resources or a complete daemon crash. This behavior falls under CWE-835, which describes infinite loops or iterations that do not terminate properly, and represents a classic example of a resource exhaustion vulnerability that can be exploited for denial of service attacks.
The operational impact of this vulnerability extends beyond simple service disruption, as it can compromise the integrity of time synchronization services that many critical network operations depend upon. When ntpd crashes or enters an infinite loop, network devices lose their ability to maintain accurate time synchronization, which can affect logging consistency, authentication mechanisms, certificate validation, and various time-sensitive network protocols. The vulnerability is particularly dangerous in environments where precise timekeeping is essential for security operations, as it can create windows of opportunity for other attacks that rely on time-based validation or temporal consistency.
Mitigation strategies for CVE-2015-7850 should prioritize immediate patching of affected ntpd installations to versions 4.2.8p4 or 4.3.77, which contain the necessary code modifications to prevent key file references from pointing to log file locations. System administrators should also implement strict configuration management practices that validate file paths and prevent unauthorized modifications to critical service configuration files. Additionally, network monitoring solutions should be configured to detect unusual resource consumption patterns or service restarts that might indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability aligns with techniques targeting service availability through resource exhaustion and process manipulation, making it a critical consideration for organizations implementing defensive security measures. The vulnerability demonstrates the importance of proper input validation and configuration file handling in network services, particularly those that operate with elevated privileges and maintain persistent system services.