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Medium severity6.5NVD Advisory· Published Jan 30, 2017· Updated May 13, 2026

CVE-2015-7973

CVE-2015-7973

Description

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.

AI Insight

LLM-synthesized narrative grounded in this CVE's description and references.

NTP broadcast mode replay attack allows MITM to replay authenticated broadcast packets, affecting NTP before 4.2.8p6 and 4.3.x before 4.3.90.

Vulnerability

NTP versions before 4.2.8p6 and 4.3.x before 4.3.90, when configured in broadcast mode, are vulnerable to a replay attack. An attacker on the network can capture authenticated broadcast packets and replay them to clients, bypassing authentication checks. This issue is identified as CVE-2015-7973 and is also known as the "Deja Vu" attack [1][4].

Exploitation

An attacker must be positioned as a man-in-the-middle on the network path between the NTP server and its clients to sniff broadcast packets. No authentication or special privileges are required; the attacker only needs network access to record and later replay the captured packets [4]. The attack does not require decryption or modification of the packets.

Impact

Successful replay allows the attacker to inject stale or arbitrary time information to clients, potentially causing time shifts. This can disrupt time-sensitive services and protocols that rely on accurate NTP synchronization, but does not lead to code execution or direct data compromise. The impact is on the integrity of time synchronization [1][4].

Mitigation

Upgrade to NTP 4.2.8p6 or later, or 4.3.90 or later. Cisco has released software updates for affected products [1]. FreeBSD has also provided patches in its security advisory [3]. If an upgrade is not immediately possible, disable broadcast mode or use symmetric key authentication with unique keys per client to mitigate the risk [4].

References
  1. Cisco Security Advisory: Multiple Vulnerabilities in Network Time Protocol Daemon Affecting Cisco Products: January 2016
  2. https://security.FreeBSD.org/advisories/FreeBSD-SA-16:09.ntp.asc
  3. CERT/CC Vulnerability Note VU#718152

AI Insight generated on May 23, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.

Affected products

103

Patches

0

No patches discovered yet.

Vulnerability mechanics

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References

22

News mentions

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