CVE-2016-4954 in ntpd
Summary
by MITRE
The process_packet function in ntp_proto.c in ntpd in NTP 4.x before 4.2.8p8 allows remote attackers to cause a denial of service (peer-variable modification) by sending spoofed packets from many source IP addresses in a certain scenario, as demonstrated by triggering an incorrect leap indication.
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Analysis
by VulDB Data Team • 12/22/2024
The vulnerability described in CVE-2016-4954 affects the Network Time Protocol daemon implementation in NTP versions prior to 4.2.8p8, specifically within the process_packet function located in ntp_proto.c. This flaw represents a significant denial of service weakness that can be exploited by remote attackers to manipulate peer variables and disrupt time synchronization services. The vulnerability stems from insufficient validation of incoming packets, particularly when multiple spoofed packets are received from various source IP addresses, creating a scenario where legitimate time synchronization operations become compromised.
The technical exploitation of this vulnerability occurs through a specific attack pattern involving spoofed packets originating from numerous source IP addresses. When ntpd processes these packets, the flawed validation logic in process_packet function fails to properly handle the peer variable modifications that result from such spoofed traffic. This particular scenario can trigger an incorrect leap indication, which is a critical time synchronization parameter that indicates when a leap second should be inserted into the time stream. The improper handling of these peer variables leads to a denial of service condition where the NTP daemon becomes unable to maintain accurate time synchronization with its peers, effectively disrupting network time services for all systems relying on that particular NTP server.
From an operational impact perspective, this vulnerability can severely compromise time synchronization services across networks that depend on affected NTP implementations. The denial of service condition affects not only the immediate NTP server but can cascade through interconnected systems that rely on accurate timekeeping for security logging, authentication mechanisms, and timestamped data operations. The attack requires minimal resources from the attacker since it leverages spoofed packets from multiple IP addresses, making it difficult to trace and mitigate. The vulnerability specifically targets the leap second handling mechanism, which is a fundamental aspect of time synchronization protocols and can cause widespread disruption when compromised.
The weakness aligns with CWE-20, which describes improper input validation, and specifically relates to CWE-399, which covers resource management errors. This vulnerability also maps to ATT&CK technique T1499.001, which covers network denial of service attacks, and T1566.001, which covers spearphishing attachments, as attackers may use spoofed packets to gain control over network time services. The vulnerability demonstrates a critical flaw in the peer management logic within NTP implementations, where the system fails to properly validate packet sources and their associated peer variables. Organizations should implement immediate mitigations including updating to NTP version 4.2.8p8 or later, which contains the necessary patches to validate peer variables properly and prevent spoofed packet manipulation. Additional network-level protections such as rate limiting and packet filtering can provide supplementary defense in depth measures to protect against similar variants of this class of vulnerability.