CVE-2015-7871 in ntpd
Summary
by MITRE
Crypto-NAK packets in ntpd in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows remote attackers to bypass authentication.
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Analysis
by VulDB Data Team • 06/24/2022
The vulnerability identified as CVE-2015-7871 represents a critical flaw in the Network Time Protocol daemon implementation that affects versions of NTP 4.2.x prior to 4.2.8p4 and 4.3.x prior to 4.3.77. This issue resides within the handling of Crypto-NAK packets, which are specifically designed to provide authentication mechanisms for time synchronization processes. The vulnerability allows remote attackers to bypass authentication controls that should normally prevent unauthorized time synchronization operations, creating a significant security risk for systems relying on NTP for time coordination.
The technical flaw manifests in the improper validation of Crypto-NAK packets within the ntpd daemon's authentication processing logic. When the daemon receives these packets, it fails to properly verify the cryptographic integrity of the authentication data, enabling attackers to craft malicious packets that appear legitimate to the system. This weakness falls under the category of authentication bypass vulnerabilities, specifically related to improper input validation and cryptographic protocol implementation. The vulnerability is classified as CWE-287, which addresses improper authentication mechanisms in network protocols, and aligns with ATT&CK technique T1562.001 for "Tactics and Techniques of the Adversary" related to privilege escalation through protocol manipulation.
The operational impact of this vulnerability extends beyond simple authentication bypass, as it allows attackers to potentially manipulate time synchronization across networked systems. This can lead to cascading security issues including certificate validation failures, log timestamp manipulation, and disruption of time-sensitive security operations. The remote nature of the attack means that adversaries can exploit this vulnerability from outside the network perimeter without requiring local access or credentials, making it particularly dangerous for organizations that rely on NTP for critical infrastructure time synchronization. The vulnerability is especially concerning in environments where precise timekeeping is essential for security operations such as intrusion detection systems, security information and event management systems, and cryptographic operations.
Mitigation strategies for CVE-2015-7871 require immediate patching of affected NTP implementations to versions 4.2.8p4 or 4.3.77 and later. Organizations should also implement network segmentation and access controls to limit exposure of NTP servers to untrusted networks. Additional defensive measures include monitoring for unusual NTP traffic patterns, implementing strict firewall rules that restrict NTP traffic to authorized sources only, and deploying intrusion detection systems that can identify potential exploitation attempts. The vulnerability demonstrates the critical importance of maintaining up-to-date network protocols and highlights the need for comprehensive security testing of authentication mechanisms. Organizations should also consider implementing time synchronization redundancy measures and alternative time sources to reduce dependency on potentially compromised NTP servers. This vulnerability serves as a reminder of the security implications inherent in network time synchronization protocols and the necessity of robust cryptographic implementation in critical infrastructure components.