CVE-2015-7979 in ntp
Summary
by MITRE
NTP before 4.2.8p6 and 4.3.x before 4.3.90 allows remote attackers to cause a denial of service (client-server association tear down) by sending broadcast packets with invalid authentication to a broadcast client.
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Analysis
by VulDB Data Team • 07/06/2022
The vulnerability described in CVE-2015-7979 represents a significant denial of service weakness in the Network Time Protocol implementation that affects versions prior to 4.2.8p6 and 4.3.x before 4.3.90. This issue specifically targets broadcast clients that are configured to receive time synchronization packets from multiple sources, creating a scenario where malicious actors can exploit the authentication handling mechanism to disrupt time synchronization services. The vulnerability stems from insufficient validation of broadcast packets received by NTP clients, particularly when these packets contain invalid authentication data that should normally be rejected by the protocol's security mechanisms.
The technical flaw manifests when a broadcast client processes incoming broadcast packets that contain malformed or invalid authentication information. Under normal circumstances, NTP clients should reject packets that fail authentication checks to prevent unauthorized time synchronization attempts and maintain network integrity. However, in vulnerable versions of NTP, the client fails to properly handle these invalid authentication packets, leading to a cascade of events that results in the client tearing down its association with the time server. This behavior occurs because the client interprets the invalid authentication data as a security threat and subsequently terminates the time synchronization session, effectively removing the client from the time synchronization network.
The operational impact of this vulnerability extends beyond simple service disruption, as it can compromise the reliability of time synchronization across entire networks that depend on NTP for coordinated operations. When a broadcast client experiences this denial of service condition, it can affect downstream systems that rely on accurate timekeeping for logging, security event correlation, network authentication, and various time-sensitive applications. The vulnerability is particularly concerning because it can be exploited remotely without requiring authentication or specialized privileges, making it accessible to any attacker who can send packets to the affected network segment. This remote exploit capability means that attackers can target NTP clients from outside the network perimeter, potentially causing widespread disruption to time-sensitive services.
Network administrators and security professionals should consider this vulnerability in the context of the broader NTP security landscape and its alignment with various attack patterns documented in the MITRE ATT&CK framework. The vulnerability relates to techniques involving protocol manipulation and service disruption, which fall under the broader category of network service denial of service attacks. From a CWE perspective, this issue corresponds to weakness categories involving improper input validation and inadequate error handling in network protocols. The vulnerability demonstrates how seemingly minor flaws in authentication handling can lead to significant operational impacts, particularly in environments where time synchronization is critical for security operations and system coordination.
Mitigation strategies for CVE-2015-7979 primarily focus on upgrading to patched versions of NTP software, specifically versions 4.2.8p6 or later for the 4.2.x series and 4.3.90 or later for the 4.3.x series. Organizations should also implement network segmentation and access control measures to limit exposure of NTP broadcast clients to untrusted networks. Additional protective measures include configuring NTP clients to use symmetric key authentication and implementing monitoring to detect unusual patterns of client disconnections or authentication failures. Security teams should also consider implementing network intrusion detection systems that can identify and alert on malformed NTP broadcast packets that may indicate exploitation attempts. The vulnerability highlights the importance of maintaining current security patches and the critical role of protocol security in maintaining overall network stability and reliability.