CVE-2015-7973 in ntp
Summary
by MITRE
NTP before 4.2.8p6 and 4.3.x before 4.3.90, when configured in broadcast mode, allows man-in-the-middle attackers to conduct replay attacks by sniffing the network.
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Analysis
by VulDB Data Team • 05/17/2026
The vulnerability identified as CVE-2015-7973 affects the Network Time Protocol implementation in versions prior to 4.2.8p6 and 4.3.x before 4.3.90. This issue specifically manifests when NTP is configured to operate in broadcast mode, creating a significant security weakness that exposes systems to man-in-the-middle attacks. The vulnerability stems from insufficient cryptographic protection mechanisms within the NTP protocol implementation, particularly in how it handles time synchronization broadcasts. Attackers can exploit this weakness by passively monitoring network traffic to capture NTP broadcast packets containing time synchronization data.
The technical flaw resides in the lack of proper authentication and integrity verification mechanisms within the NTP broadcast mode implementation. When NTP servers broadcast time information to clients in broadcast mode, the protocol does not adequately validate the authenticity of the time data being transmitted. This absence of cryptographic validation allows attackers positioned on the network to capture legitimate NTP broadcast messages and replay them at a later time to manipulate the time synchronization process. The vulnerability specifically impacts the NTP protocol's ability to distinguish between legitimate and malicious time data, creating an attack surface where attackers can inject false time information into the network.
The operational impact of this vulnerability extends beyond simple time synchronization issues, as incorrect time settings can compromise the security of numerous network services and protocols that rely on accurate timekeeping. Systems using NTP for authentication, logging, certificate validation, and security protocol operations become vulnerable to various attack vectors when time information is manipulated. The replay attacks enabled by this vulnerability can lead to authentication failures, certificate validation issues, and disruption of time-sensitive security operations. Organizations with multiple NTP clients and servers operating in broadcast mode face significant risk of coordinated time manipulation attacks that could go undetected for extended periods.
Mitigation strategies for CVE-2015-7973 primarily involve upgrading to patched versions of NTP software, specifically versions 4.2.8p6 or 4.3.90 and later. Organizations should also consider implementing additional network security measures such as network segmentation, intrusion detection systems, and monitoring for unusual NTP traffic patterns. The vulnerability aligns with CWE-310, which addresses cryptographic issues, and relates to ATT&CK techniques involving credential access and defense evasion through time manipulation. Network administrators should also consider disabling broadcast mode when possible and implementing symmetric key authentication or other cryptographic protections for NTP communications to prevent unauthorized modification of time data. Proper network monitoring and regular security assessments can help detect potential exploitation attempts and ensure continued protection against this and similar time synchronization vulnerabilities.