CVE-2018-8956 in ntp
Summary
by MITRE
ntpd in ntp 4.2.8p10, 4.2.8p11, 4.2.8p12 and 4.2.8p13 allow remote attackers to prevent a broadcast client from synchronizing its clock with a broadcast NTP server via soofed mode 3 and mode 5 packets. The attacker must either be a part of the same broadcast network or control a slave in that broadcast network that can capture certain required packets on the attacker's behalf and send them to the attacker.
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Analysis
by VulDB Data Team • 10/15/2020
The vulnerability described in CVE-2018-8956 represents a significant security flaw in the Network Time Protocol implementation within ntpd versions 4.2.8p10 through 4.2.8p13. This issue specifically targets the broadcast client synchronization mechanism that allows network time clients to automatically synchronize their clocks with designated broadcast NTP servers. The vulnerability enables remote attackers to disrupt legitimate time synchronization processes through the manipulation of specific NTP packet types, creating a denial of service condition that affects the accuracy and reliability of timekeeping across affected networks.
The technical flaw stems from insufficient validation of NTP mode 3 and mode 5 packets received by broadcast clients during the synchronization process. These packet types contain critical timing information that must be verified before being accepted for clock adjustment. Attackers exploit this weakness by crafting and transmitting spoofed packets that appear legitimate to the broadcast client but contain maliciously altered data or timing parameters. The vulnerability requires the attacker to either exist within the same broadcast network segment or control a slave node that can intercept and relay the necessary packets to the attacker, establishing a sophisticated attack vector that leverages network topology rather than direct system compromise.
The operational impact of this vulnerability extends beyond simple denial of service, as it fundamentally undermines the integrity of time synchronization within network environments. When exploited successfully, the vulnerability prevents broadcast clients from properly synchronizing their clocks with legitimate NTP servers, potentially causing cascading effects throughout network infrastructure that depends on accurate timekeeping for security logging, authentication mechanisms, and timestamped operations. The disruption affects not only individual client systems but can also compromise the overall network time coordination, potentially leading to authentication failures, security event misalignment, and compliance violations in regulated environments. This vulnerability particularly impacts systems where precise time synchronization is critical for security operations, making it a significant concern for enterprise networks, financial institutions, and government agencies.
Mitigation strategies for CVE-2018-8956 should focus on both immediate patching and network-level defenses. Organizations must upgrade to ntp versions that address this vulnerability, specifically ntp 4.2.8p14 or later, which contain fixes for the packet validation issues. Network segmentation and access control measures should be implemented to limit broadcast network exposure and prevent unauthorized access to broadcast client systems. The implementation of NTP authentication mechanisms, including symmetric key authentication or trusted key systems, provides additional protection against spoofed packet manipulation. According to CWE classification, this vulnerability relates to CWE-290: Authentication Bypass by Spoofing, while ATT&CK framework references T1071.004: Application Layer Protocol: DNS and T1566.001: Phishing: Spearphishing Attachment, as attackers may need to establish network presence to conduct the attack. Network monitoring should be enhanced to detect anomalous NTP packet patterns and unauthorized time synchronization attempts, while system administrators should implement regular security assessments to identify and remediate similar vulnerabilities in time synchronization infrastructure.