CVE-2023-26551 in NTP
Summary
by MITRE • 04/12/2023
mstolfp in libntp/mstolfp.c in NTP 4.2.8p15 has an out-of-bounds write in the cp<cpdec while loop.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 04/29/2026
The vulnerability identified as CVE-2023-26551 resides within the Network Time Protocol implementation in NTP 4.2.8p15, specifically within the mstolfp function located in libntp/mstolfp.c. This issue manifests as an out-of-bounds write condition that occurs during the execution of a while loop labeled cp<cpdec. The flaw represents a critical security concern that could potentially allow remote attackers to execute arbitrary code or cause system instability through carefully crafted network packets.
The technical root cause of this vulnerability stems from improper bounds checking within the cp<cpdec loop structure. When processing time synchronization data, the mstolfp function fails to validate array indices or buffer limits before writing data to memory locations. This allows an attacker to manipulate input parameters such that the write operation extends beyond the allocated memory boundaries, potentially overwriting adjacent memory regions. The vulnerability is classified as a buffer overflow condition that aligns with CWE-121, which describes stack-based buffer overflow issues, and more specifically relates to CWE-787, which addresses out-of-bounds write conditions in heap-based memory structures.
From an operational perspective, this vulnerability presents significant risks to network infrastructure relying on NTP services for time synchronization. The out-of-bounds write could enable attackers to corrupt process memory, leading to denial of service conditions or potentially allowing remote code execution. Systems that depend on accurate timekeeping for security operations, such as authentication mechanisms, log correlation, and cryptographic operations, could experience cascading failures. The vulnerability is particularly concerning because it operates at the protocol level, meaning that any device or service communicating over NTP could be affected, including network switches, routers, servers, and embedded systems.
The impact of this vulnerability extends beyond immediate system compromise, as it could facilitate more sophisticated attacks within network environments. According to ATT&CK framework reference T1071.004, this vulnerability could be leveraged for protocol manipulation and could potentially be used as a stepping stone for lateral movement within networks where NTP services are widely deployed. Organizations using NTP implementations that are vulnerable to CVE-2023-26551 should consider the broader implications for their network security posture, as this flaw could be exploited in conjunction with other vulnerabilities to establish persistent access or disrupt critical time-sensitive operations.
Mitigation strategies for CVE-2023-26551 should prioritize immediate patching of affected NTP implementations to version 4.2.8p16 or later, which includes the necessary bounds checking fixes. Network administrators should implement monitoring for unusual NTP traffic patterns that might indicate exploitation attempts, while also considering network segmentation to limit the potential impact of successful attacks. Additional defensive measures include implementing strict NTP access controls, deploying intrusion detection systems that can identify malformed NTP packets, and conducting regular security assessments of time synchronization infrastructure. Organizations should also verify that their NTP implementations are properly configured to prevent unnecessary exposure to external networks and ensure that all systems are regularly updated to address known vulnerabilities in time synchronization protocols.