CVE-2016-7433 in ntpd
Summary
by MITRE
NTP before 4.2.8p9 does not properly perform the initial sync calculations, which allows remote attackers to unspecified impact via unknown vectors, related to a "root distance that did not include the peer dispersion."
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Analysis
by VulDB Data Team • 05/13/2026
The vulnerability identified as CVE-2016-7433 affects the Network Time Protocol implementation in versions prior to 4.2.8p9, representing a critical flaw in time synchronization mechanisms that underpin network security infrastructure. This issue stems from improper handling of initial synchronization calculations within the NTP daemon, specifically concerning how the root distance is computed during the time synchronization process. The root distance calculation is fundamental to NTP's trust model, as it determines the maximum possible error in time measurements between peers and the reference time source. When peer dispersion is not properly included in the root distance calculation, the system can incorrectly assess the reliability and accuracy of time sources, potentially leading to malicious actors manipulating time synchronization behavior. The vulnerability's impact extends beyond simple timekeeping issues, as it can compromise the integrity of time-sensitive security protocols that depend on accurate NTP implementations.
The technical flaw manifests in the NTP protocol's initial synchronization algorithm where the peer dispersion component, which represents the statistical variance in network delays between time sources, is excluded from the root distance calculation. This omission creates a scenario where a malicious attacker could exploit the system's trust model by presenting false time data that appears legitimate due to the incomplete distance calculations. The vulnerability operates through the NTP client-server interaction model where peers exchange time information and compute their collective accuracy based on statistical measures. When peer dispersion is not factored into the root distance, the system may incorrectly accept time sources that have been manipulated or compromised, potentially leading to time drift or even complete time synchronization failure. This flaw aligns with CWE-200, which addresses improper handling of sensitive information, and specifically relates to weaknesses in information flow and data validation within network protocols.
The operational impact of CVE-2016-7433 extends significantly across network security infrastructure, particularly affecting systems that rely heavily on precise time synchronization for authentication mechanisms, log correlation, and cryptographic operations. Security systems dependent on NTP for time stamping, such as intrusion detection systems, security information and event management platforms, and certificate validation processes, could experience complete failure or manipulation of time-based security controls. The vulnerability enables attackers to perform time-based attacks that could bypass time-sensitive security controls, potentially allowing for credential theft, session hijacking, or bypassing time-based access controls. From an adversarial perspective, this vulnerability can be leveraged in conjunction with other attack vectors within the MITRE ATT&CK framework, particularly under the T1562.001 technique related to "Impairing Security Tools" and T1078.001 "Valid Accounts" where compromised time synchronization could facilitate further malicious activities.
Mitigation strategies for CVE-2016-7433 primarily involve immediate upgrading to NTP version 4.2.8p9 or later, which includes the corrected root distance calculation that properly incorporates peer dispersion values. Organizations should also implement additional monitoring of NTP synchronization behavior, particularly watching for unusual time drift patterns or unexpected peer selection decisions that might indicate exploitation attempts. Network administrators should configure NTP servers with proper authentication mechanisms, including symmetric key authentication or NTPv4 authentication, to prevent unauthorized manipulation of time sources. Security teams should establish baseline NTP behavior monitoring and alerting systems that can detect when peer dispersion values are not being properly accounted for in time calculations. The vulnerability's remediation aligns with industry best practices for protocol security and follows the principle of least privilege in time synchronization implementations. Organizations should also consider implementing redundant time synchronization sources and regularly auditing their NTP configurations to ensure proper dispersion handling and overall time synchronization integrity.