CVE-2015-7692 in ntpd
Summary
by MITRE
The crypto_xmit function in ntpd in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows remote attackers to cause a denial of service (crash). NOTE: This vulnerability exists due to an incomplete fix for CVE-2014-9750.
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Analysis
by VulDB Data Team • 06/25/2022
The vulnerability identified as CVE-2015-7692 represents a critical denial of service flaw within the Network Time Protocol daemon implementation. This issue affects NTP versions 4.2.x prior to 4.2.8p4 and 4.3.x prior to 4.3.77, demonstrating the persistent nature of protocol implementation weaknesses that can persist across multiple releases. The vulnerability specifically resides within the crypto_xmit function of ntpd, which handles cryptographic operations during network time synchronization processes. The flaw manifests when remote attackers can trigger a crash condition that brings down the NTP daemon, effectively disrupting time synchronization services across affected systems.
The technical root cause of this vulnerability stems from an incomplete remediation of CVE-2014-9750, creating a scenario where the initial fix failed to address all potential attack vectors within the cryptographic transmission mechanism. This incomplete fix leaves the system exposed to specific input conditions that cause the crypto_xmit function to process data in a manner that leads to memory corruption or invalid state transitions. The vulnerability operates at the protocol level where network packets containing specially crafted cryptographic data can cause the ntpd process to terminate unexpectedly, creating a service disruption that can cascade through network infrastructure relying on accurate time synchronization.
From an operational perspective, this vulnerability presents significant risk to network infrastructure stability and availability. When exploited, the denial of service condition can cause the NTP daemon to crash and restart automatically, potentially disrupting time synchronization across multiple network devices and services that depend on accurate timekeeping. The impact extends beyond simple service interruption as many network security systems, authentication mechanisms, and logging services rely on synchronized time stamps to function correctly. The vulnerability's remote exploitability means that attackers can trigger the condition without requiring local access, making it particularly dangerous in network environments where external connectivity is common.
The vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and reflects patterns commonly found in cryptographic protocol implementations where input validation and memory management are critical. From the MITRE ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to network denial of service, and could potentially be leveraged as part of broader attack campaigns targeting network infrastructure. The lack of proper input sanitization in the crypto_xmit function creates an exploitation pathway that allows attackers to manipulate the execution flow of the NTP daemon through crafted network packets.
Organizations should prioritize immediate patching of affected NTP installations to address this vulnerability, as the incomplete fix for CVE-2014-9750 created a persistent weakness that attackers can exploit. The recommended mitigation strategy involves upgrading to NTP versions 4.2.8p4 or later for 4.2.x releases, and 4.3.77 or later for 4.3.x releases, where comprehensive fixes have been implemented. Network administrators should also consider implementing network segmentation and access controls to limit exposure to potentially malicious traffic, while monitoring for unusual network behavior that might indicate exploitation attempts. The vulnerability serves as a reminder of the importance of complete vulnerability remediation and the potential consequences of partial fixes in security-critical network services.