CVE-2019-8936 in ntp
Summary
by MITRE
NTP through 4.2.8p12 has a NULL Pointer Dereference.
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Analysis
by VulDB Data Team • 09/21/2023
The vulnerability identified as CVE-2019-8936 represents a critical null pointer dereference flaw within the Network Time Protocol implementation version 4.2.8p12 and earlier. This issue affects the ntpd daemon which is responsible for synchronizing system clocks across networked devices, making it a significant concern for network infrastructure security. The vulnerability arises from insufficient input validation and error handling within the protocol processing logic, specifically when handling malformed time synchronization requests from remote hosts. When a malicious actor sends specially crafted NTP packets containing null pointers in critical data structures, the daemon attempts to dereference these invalid pointers, leading to a system crash and potential denial of service condition. This vulnerability directly maps to CWE-476 which describes NULL Pointer Dereference, a well-known weakness in software development that occurs when a program attempts to access memory through a null pointer reference. The impact extends beyond simple service disruption as this vulnerability can be exploited remotely without authentication, making it particularly dangerous in networked environments where time synchronization services are critical for system operations.
The operational impact of CVE-2019-8936 manifests as a remote denial of service condition that can bring down time synchronization services across affected networks. When exploited successfully, the null pointer dereference causes the ntpd process to terminate abruptly, forcing systems to lose time synchronization capabilities until manual intervention occurs. This disruption can cascade through network infrastructure as time synchronization is fundamental for security logging, authentication systems, and coordinated network operations. The vulnerability's exploitability is enhanced by the fact that NTP typically runs on well-known ports and is often exposed to untrusted networks, making it accessible to attackers without requiring privileged access. From an attack perspective, this vulnerability aligns with ATT&CK technique T1499.001 which describes Network Denial of Service attacks, and T1566 which covers spearphishing through social engineering. The flaw demonstrates poor defensive programming practices where proper validation of incoming network data was not implemented, allowing malformed input to propagate into critical system functions.
Mitigation strategies for CVE-2019-8936 should focus on immediate patching of affected ntpd implementations to version 4.2.8p13 or later, which contains the necessary fixes for the null pointer dereference issue. Network administrators should implement firewall rules to restrict NTP traffic to trusted sources only, limiting exposure of time synchronization services to external networks. Additionally, monitoring systems should be configured to detect abnormal ntpd process behavior or frequent restarts that might indicate exploitation attempts. The vulnerability highlights the importance of input validation and robust error handling in network services, principles that align with security standards such as those outlined in the OWASP Top Ten and NIST SP 800-53. Organizations should also consider implementing intrusion detection systems that can identify suspicious NTP traffic patterns and deploy network segmentation strategies to isolate critical time synchronization infrastructure from potentially compromised segments. Regular security assessments and vulnerability scanning should include checks for outdated NTP implementations to prevent similar issues from arising in the future, as this vulnerability represents a common class of flaws that can be prevented through proper defensive programming practices and comprehensive security testing procedures.