CVE-2018-7170 in ntp
Summary
by MITRE
nptd in ntp 4.2.x before 4.2.8p7 and 4.3.x before 4.3.92 allows authenticated users that know the private symmetric key to create arbitrarily-many ephemeral associations in order to win the clock selection of ntpd and modify a victim's clock via a Sybil attack. This issue exists because of an incomplete fix for CVE-2016-1549.
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Analysis
by VulDB Data Team • 01/15/2025
The vulnerability described in CVE-2018-7170 represents a significant security flaw in the Network Time Protocol implementation within ntpd versions prior to 4.2.8p7 and 4.3.92. This issue specifically targets the nptd component which handles symmetric key authentication for time synchronization operations. The vulnerability enables authenticated attackers who possess knowledge of the private symmetric key to exploit a weakness in the clock selection mechanism that allows them to create an unlimited number of ephemeral associations. This capability directly enables a Sybil attack pattern where the malicious actor can overwhelm legitimate time sources and manipulate the victim's system clock through the ntpd process. The flaw is particularly concerning because it builds upon an earlier vulnerability CVE-2016-1549 which was previously addressed but not completely resolved, leaving a persistent weakness in the authentication and association management system. The vulnerability operates within the context of time synchronization protocols where ntpd maintains multiple associations with time servers and selects the most reliable source based on various criteria including stratum levels, delay measurements, and other statistical factors that determine clock accuracy.
The technical implementation of this vulnerability stems from insufficient validation mechanisms within the ntpd association management system. When authenticated users with knowledge of the private symmetric key create multiple ephemeral associations, the system fails to properly rate limit or authenticate these connections effectively. This allows an attacker to flood the ntpd process with numerous fake associations that can artificially influence the clock selection algorithm. The attack exploits the fact that ntpd uses a weighted selection process where multiple associations contribute to the final time calculation, and by creating many fake associations, the attacker can manipulate the statistical outcomes to favor their malicious time source. The incomplete fix for CVE-2016-1549 means that while some protections were implemented, the fundamental issue of association proliferation was not fully addressed, leaving the system vulnerable to resource exhaustion attacks that can ultimately result in clock manipulation. This flaw specifically relates to CWE-307 which addresses inadequate protection against excessive resource consumption, and also maps to ATT&CK technique T1496 which covers resource hijacking through time synchronization manipulation.
The operational impact of CVE-2018-7170 extends beyond simple clock drift manipulation and can result in significant security implications for systems relying on accurate timekeeping. When successful, this attack can cause legitimate time sources to be ignored or overridden, potentially leading to time-based authentication failures, certificate validation issues, and disruption of time-sensitive security operations. The ability to manipulate a victim's clock can compromise the integrity of log timestamps, affect security audits, and undermine the trust model of time-dependent cryptographic operations. Systems that depend on ntpd for time synchronization including network infrastructure devices, security appliances, and enterprise servers become vulnerable to this type of manipulation. The vulnerability also affects the broader security ecosystem because many security protocols and services rely on synchronized time for proper operation, including Kerberos authentication, SSL/TLS certificate validation, and various network security monitoring systems. Organizations running vulnerable ntpd versions face the risk of sophisticated attacks where time manipulation becomes a vector for broader system compromise, as the attack can be used to bypass time-based security controls and create false timelines for forensic analysis.
Mitigation strategies for CVE-2018-7170 require immediate deployment of patched ntpd versions including 4.2.8p7 and 4.3.92 or later releases that contain the complete fix for this vulnerability. Organizations should also implement network-level restrictions to limit the number of time associations that can be established, particularly for systems that do not require multiple time sources. The implementation of rate limiting mechanisms within ntpd configuration files can help restrict the creation of ephemeral associations by authenticated users. Network administrators should also consider implementing monitoring solutions that can detect unusual patterns of association creation and clock manipulation attempts. Additional protective measures include restricting access to the private symmetric keys and implementing more robust authentication mechanisms that prevent unauthorized users from establishing authenticated connections. The fix addresses the underlying CWE-307 weakness by implementing proper resource management and rate limiting for association creation. Security teams should also review their time synchronization configurations to ensure that systems are not unnecessarily configured to accept multiple time sources from untrusted networks, and consider implementing more restrictive access controls for ntpd operations that can be exploited by authenticated users. Regular security assessments of time synchronization infrastructure should be conducted to identify and remediate similar vulnerabilities that may exist in other network services relying on similar association and authentication mechanisms.