CVE-2015-7702 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-2015-7702 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-level security concerns in time synchronization systems. The vulnerability specifically resides within the crypto_xmit function of ntpd, which handles cryptographic operations during network communication. The flaw emerged as an incomplete remediation of a previously addressed vulnerability, CVE-2014-9750, indicating that security patches may not always fully resolve underlying architectural issues.
The technical implementation of the vulnerability stems from improper handling of cryptographic message transmission within the NTP protocol stack. When remote attackers send specially crafted packets to an affected NTP daemon, the crypto_xmit function fails to properly validate or process these inputs, leading to a crash condition that terminates the ntpd process. This function operates within the cryptographic subsystem of NTP, managing the transmission of time synchronization messages that require secure handling of authentication tokens and cryptographic signatures. The incomplete fix for CVE-2014-9750 left residual conditions in the code path that governs how the daemon processes these cryptographic messages, creating an exploitable state where malformed inputs can trigger memory corruption or invalid state transitions.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged by attackers to systematically disable time synchronization services across affected networks. Network time protocol daemons serve as critical infrastructure components for maintaining accurate time across distributed systems, and their compromise can cascade into broader operational failures. When an ntpd process crashes due to this vulnerability, it not only stops time synchronization for the affected host but can also trigger cascading failures in systems that depend on accurate timekeeping for security operations, database transactions, and log correlation. The vulnerability's remote exploitability means that attackers can target these services from outside the network perimeter, making it particularly dangerous in enterprise environments where time synchronization services are exposed to external traffic.
Organizations affected by CVE-2015-7702 should prioritize immediate patching of their NTP implementations to version 4.2.8p4 or 4.3.77, which contain the complete remediation for both the original vulnerability and its incomplete fix. The mitigation strategy should also include network segmentation to limit exposure of NTP services to untrusted networks and implementing monitoring for unusual ntpd process restarts or crash patterns. From a security framework perspective, this vulnerability aligns with CWE-248, representing an unchecked exception in a cryptographic operation, and demonstrates techniques that could be categorized under ATT&CK tactic TA0040 (Resource Hijacking) and technique T1499.001 (Endpoint Denial of Service). The vulnerability also highlights the importance of proper input validation in cryptographic libraries and the need for comprehensive regression testing when implementing security patches to ensure that previous fixes do not introduce new attack surfaces.