CVE-2016-2517 in ntp
Summary
by MITRE
NTP before 4.2.8p7 and 4.3.x before 4.3.92 allows remote attackers to cause a denial of service (prevent subsequent authentication) by leveraging knowledge of the controlkey or requestkey and sending a crafted packet to ntpd, which changes the value of trustedkey, controlkey, or requestkey. NOTE: this vulnerability exists because of a CVE-2016-2516 regression.
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Analysis
by VulDB Data Team • 07/27/2022
The vulnerability described in CVE-2016-2517 represents a critical denial of service weakness in the Network Time Protocol implementation that affects versions prior to 4.2.8p7 and 4.3.x prior to 4.3.92. This issue specifically targets the ntpd daemon's handling of cryptographic keys used for authentication and control operations. The flaw stems from a regression introduced by CVE-2016-2516, which inadvertently created a path for remote attackers to manipulate the daemon's key management system. The vulnerability operates through a sophisticated attack vector where an adversary with knowledge of existing controlkey or requestkey values can craft malicious packets to influence the trustedkey, controlkey, or requestkey values within the ntpd process. This regression essentially undermines the security model that ntpd employs to maintain authentication integrity and control access to time synchronization services.
The technical implementation of this vulnerability exploits the ntpd daemon's key handling mechanisms by leveraging the fact that certain key values can be modified through crafted network packets when the attacker possesses valid key knowledge. When an attacker sends specifically crafted packets containing manipulated key values, the ntpd daemon processes these inputs without sufficient validation, allowing the attacker to effectively change the values of trustedkey, controlkey, or requestkey parameters. This modification fundamentally disrupts the authentication chain that ntpd relies upon for secure time synchronization operations. The daemon's response to these crafted packets results in a state where subsequent authentication attempts fail because the key values have been altered, creating a persistent denial of service condition that prevents legitimate users from establishing proper time synchronization connections.
The operational impact of CVE-2016-2517 extends beyond simple service disruption to create a comprehensive compromise of network time synchronization infrastructure. When exploited successfully, this vulnerability creates a persistent state where legitimate time synchronization services become unavailable, forcing network systems to either fall back to alternative time sources or remain unsynchronized. The vulnerability is particularly dangerous because it can be exploited remotely without requiring authentication, making it an attractive target for attackers seeking to disrupt network operations. The regression aspect of this vulnerability means that security updates or patches addressing CVE-2016-2516 may have inadvertently introduced this weakness, creating a scenario where systems thought to be secure against previous vulnerabilities become vulnerable to this specific denial of service attack. Organizations relying on ntpd for time synchronization across critical infrastructure components face significant risk of operational disruption when this vulnerability is exploited.
Mitigation strategies for CVE-2016-2517 require immediate deployment of patched ntpd versions that address both the original CVE-2016-2516 regression and the subsequent vulnerability. System administrators should ensure that all ntpd instances are updated to versions 4.2.8p7 or later for the 4.2.x series, or 4.3.92 or later for the 4.3.x series. Additionally, network segmentation and access controls should be implemented to limit exposure of ntpd services to untrusted networks, reducing the attack surface available to potential adversaries. The implementation of network monitoring solutions that can detect anomalous packet patterns related to key manipulation attempts provides an additional layer of defense. Organizations should also review their key management practices to ensure that controlkey and requestkey values are properly secured and regularly rotated. This vulnerability aligns with CWE-284 access control weaknesses and can be mapped to ATT&CK technique T1499.001 for network denial of service attacks. Regular security audits of time synchronization infrastructure and proper configuration management practices are essential for preventing exploitation of this and similar vulnerabilities.