CVE-2015-1853 in Chrony
Summary
by MITRE
chrony before 1.31.1 does not properly protect state variables in authenticated symmetric NTP associations, which allows remote attackers with knowledge of NTP peering to cause a denial of service (inability to synchronize) via random timestamps in crafted NTP data packets.
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Analysis
by VulDB Data Team • 11/29/2024
The vulnerability identified as CVE-2015-1853 affects chrony versions prior to 1.31.1 and represents a critical flaw in the network time synchronization protocol implementation. This issue specifically targets the authenticated symmetric NTP associations mechanism, which is designed to establish secure time synchronization between network peers through mutual authentication. The flaw resides in how chrony handles state variables during these authenticated sessions, creating a pathway for malicious actors to exploit the system's time synchronization capabilities. The vulnerability operates within the broader context of network time protocol security, where maintaining accurate time synchronization is crucial for system integrity and security operations across distributed networks.
The technical implementation flaw stems from insufficient protection of state variables within the authenticated symmetric NTP association process. When chrony processes NTP data packets containing crafted timestamps, it fails to properly validate or sanitize these values before updating its internal state variables. This weakness allows attackers who have gained knowledge of legitimate NTP peering relationships to inject malicious data packets with random timestamps that disrupt the normal synchronization process. The vulnerability specifically targets the state management mechanisms that track association parameters, peer information, and synchronization state, enabling attackers to manipulate these values in ways that cause the system to become unable to maintain proper time synchronization. This issue falls under the CWE category of insufficient protection of state variables, which is classified as a fundamental weakness in software design that can lead to various security implications.
The operational impact of this vulnerability extends beyond simple denial of service, as it can severely compromise the reliability of time synchronization services across network infrastructure. When exploited successfully, the vulnerability causes chrony to become unable to synchronize time with other peers, effectively rendering the affected system unable to maintain accurate time measurements. This disruption can have cascading effects on security systems that depend on synchronized time for log correlation, certificate validation, authentication protocols, and other time-sensitive operations. The attack requires only knowledge of existing NTP peering relationships, making it particularly dangerous as it can be executed by attackers who have already established some level of network access or monitoring capability. This vulnerability directly impacts the availability and integrity of time synchronization services, which are fundamental to network security operations and can be classified under the ATT&CK technique of Denial of Service through manipulation of system resources.
Mitigation strategies for CVE-2015-1853 primarily focus on upgrading to chrony version 1.31.1 or later, which includes proper state variable protection mechanisms. Organizations should also implement network segmentation and access controls to limit which systems can participate in NTP peering relationships, reducing the attack surface for potential exploitation. Additional defensive measures include monitoring NTP traffic for anomalous timestamp patterns, implementing intrusion detection systems that can identify crafted NTP packets, and establishing network access controls that restrict NTP peer relationships to trusted entities only. The vulnerability highlights the importance of proper state management in security-critical applications and demonstrates the necessity of validating all external inputs, particularly in protocols where state consistency is crucial for system operation. Organizations should also consider implementing time synchronization redundancy measures and monitoring systems to detect when time synchronization services become unavailable due to such attacks.