CVE-2016-1548 in Exalogic Infrastructure
Summary
by MITRE
An attacker can spoof a packet from a legitimate ntpd server with an origin timestamp that matches the peer->dst timestamp recorded for that server. After making this switch, the client in NTP 4.2.8p4 and earlier and NTPSec aa48d001683e5b791a743ec9c575aaf7d867a2b0c will reject all future legitimate server responses. It is possible to force the victim client to move time after the mode has been changed. ntpq gives no indication that the mode has been switched.
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Analysis
by VulDB Data Team • 04/20/2025
The vulnerability described in CVE-2016-1548 represents a sophisticated man-in-the-middle attack targeting the Network Time Protocol implementation in ntpd versions 4.2.8p4 and earlier, as well as NTPSec versions up to commit aa48d001683e5b791a743ec9c575aaf7d867a2b0c. This flaw specifically exploits the trust relationship between NTP clients and servers, creating a scenario where an attacker can manipulate time synchronization processes through carefully crafted packet spoofing. The vulnerability operates by leveraging the NTP protocol's timestamp handling mechanisms, particularly focusing on the peer->dst timestamp correlation that clients use to validate server responses. When an attacker successfully spoofs a packet from a legitimate ntpd server, they can manipulate the client's internal state to reject all subsequent legitimate responses from that server, effectively breaking the time synchronization process.
The technical implementation of this vulnerability stems from inadequate validation of timestamp consistency within the NTP protocol stack. The flaw occurs when an attacker crafts a malicious packet that appears to originate from a legitimate server, with an origin timestamp that exactly matches the peer->dst timestamp that the client has previously recorded for that server. This specific timestamp matching allows the attacker to bypass normal authentication and validation checks that should prevent such spoofing. The vulnerability is particularly insidious because it operates at the protocol level, making it difficult to detect through conventional network monitoring tools. The attacker essentially tricks the client into believing that a legitimate server has changed its operational mode, causing the client to reject all future communications from that server regardless of their authenticity. This behavior violates fundamental security principles outlined in the Common Weakness Enumeration (CWE) category CWE-284, which addresses improper access control in network protocols.
The operational impact of CVE-2016-1548 extends beyond simple time synchronization disruption, potentially enabling more severe attacks that compromise system security and integrity. When a client becomes convinced that a server has switched modes, it enters a state where it will reject all legitimate time responses, effectively isolating itself from accurate time sources. This condition can persist until the client is manually restarted or the malicious state is cleared, creating extended periods of time synchronization failure that can affect system logging, authentication processes, and cryptographic operations that depend on accurate time. The vulnerability particularly impacts systems where precise timekeeping is critical for security operations, as incorrect time can lead to certificate validation failures, authentication token expiration issues, and compromised audit trails. The lack of indication from ntpq tools about the mode switching further compounds the problem by making detection extremely difficult for system administrators, who may not realize that their systems are being compromised until they observe broader security issues.
Mitigation strategies for CVE-2016-1548 require both immediate patching and operational security improvements. The most effective immediate solution is upgrading to ntpd versions that contain fixes for this vulnerability, typically those released after the patching of this specific flaw. Organizations should also implement enhanced monitoring for NTP traffic patterns and timestamp anomalies that could indicate spoofing attempts. Network segmentation and access control measures can help limit the potential impact of such attacks by restricting which systems can communicate with NTP servers. The vulnerability demonstrates the importance of implementing robust timestamp validation and peer authentication mechanisms, aligning with ATT&CK framework techniques that emphasize protocol manipulation and credential theft through network-based attacks. Additional defensive measures include implementing NTP authentication using symmetric key cryptography, utilizing trusted time sources, and deploying intrusion detection systems specifically configured to monitor for NTP-related anomalies. Organizations should also consider implementing automated alerting for time synchronization failures and regular verification of system time accuracy to detect potential exploitation of this vulnerability.