CVE-2016-1550 in ntp
Summary
by MITRE
An exploitable vulnerability exists in the message authentication functionality of libntp in ntp 4.2.8p4 and NTPSec a5fb34b9cc89b92a8fef2f459004865c93bb7f92. An attacker can send a series of crafted messages to attempt to recover the message digest key.
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Analysis
by VulDB Data Team • 04/20/2025
The vulnerability described in CVE-2016-1550 represents a critical weakness in the Network Time Protocol's message authentication mechanisms, specifically within the libntp library component. This flaw affects ntp versions 4.2.8p4 and NTPSec versions up to a5fb34b9cc89b92a8fef2f459004865c93bb7f92, exposing systems that rely on NTP for time synchronization to potential cryptographic attacks. The vulnerability stems from insufficient protection mechanisms in the message authentication code, creating opportunities for adversaries to exploit the system's security controls.
The technical implementation of this vulnerability resides in the cryptographic message authentication code within libntp, which fails to properly protect the message digest keys used in NTP's security protocols. Attackers can leverage this weakness by sending carefully crafted NTP messages to the target system, attempting to perform a key recovery attack against the message authentication code. This process typically involves analyzing the patterns in authentication responses and exploiting mathematical properties of the underlying cryptographic functions to gradually reconstruct the secret key used for message verification.
The operational impact of this vulnerability extends beyond simple message authentication failures, as it fundamentally compromises the integrity and authenticity guarantees that NTP security protocols are designed to provide. When exploited successfully, attackers can manipulate time synchronization data, potentially causing cascading effects throughout network infrastructure that depends on accurate timekeeping. This includes disrupting critical services, enabling further attacks through time-based exploits, and undermining the trust model that secure NTP implementations rely upon for network security.
Security professionals should implement immediate mitigations including updating to patched versions of ntp software, disabling unnecessary NTP message authentication features when not required, and monitoring network traffic for suspicious authentication message patterns. The vulnerability aligns with CWE-310, which addresses cryptographic weaknesses in authentication mechanisms, and represents a significant concern from an attacker's perspective as outlined in ATT&CK technique T1562.001 for credential access through cryptographic attacks. Organizations should also consider implementing network segmentation to limit exposure and establish monitoring protocols to detect potential exploitation attempts against NTP services.