CVE-2017-6455 in ntp
Summary
by MITRE
NTP before 4.2.8p10 and 4.3.x before 4.3.94, when using PPSAPI, allows local users to gain privileges via a DLL in the PPSAPI_DLLS environment variable.
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Analysis
by VulDB Data Team • 09/14/2020
The vulnerability identified as CVE-2017-6455 represents a critical privilege escalation flaw within the Network Time Protocol implementation that affects versions prior to 4.2.8p10 and 4.3.x prior to 4.3.94. This issue specifically manifests when the PPSAPI (Pulse Per Second Application Programming Interface) functionality is enabled, creating a dangerous condition where local attackers can manipulate the system's privilege escalation pathways through carefully crafted environment variable manipulation. The vulnerability stems from insufficient validation of dynamic library loading mechanisms within the NTP daemon's PPSAPI implementation, allowing malicious actors to inject arbitrary code with elevated privileges.
The technical exploitation of this vulnerability occurs through manipulation of the PPSAPI_DLLS environment variable, which is designed to specify additional dynamic link libraries that should be loaded by the NTP service when PPSAPI functionality is active. When a local user can influence this environment variable, they can direct the NTP daemon to load malicious DLLs from arbitrary locations, bypassing normal security controls that would otherwise prevent privilege escalation. This flaw directly relates to CWE-427 Uncontrolled Search Path Element, where the application fails to properly validate or sanitize the search paths used for dynamic library loading, and CWE-276 Incorrect Default Permissions, as the vulnerable NTP service operates with elevated privileges while maintaining insecure default configurations.
The operational impact of CVE-2017-6455 extends beyond simple privilege escalation, as it provides attackers with a persistent foothold within affected systems that can be leveraged for further compromise. Since NTP services typically run with elevated privileges to properly synchronize system time and manage hardware timing interfaces, successful exploitation grants attackers the ability to execute code with system-level privileges. This vulnerability aligns with ATT&CK technique T1068 Privilege Escalation through the use of system services that operate with elevated permissions and the exploitation of insecure library loading mechanisms. The attack surface is particularly concerning because NTP services are commonly enabled on servers and workstations, making this vulnerability widespread across various network environments.
Organizations affected by this vulnerability should immediately implement mitigation strategies including updating to NTP versions 4.2.8p10 or 4.3.94 and later, which contain patches addressing the insecure DLL loading behavior. System administrators should also review and restrict environment variable modifications that could influence the PPSAPI_DLLS parameter, implementing proper access controls on NTP configuration files and environment settings. The vulnerability demonstrates the importance of secure coding practices around dynamic library loading and highlights the need for proper privilege separation in system services. Additionally, monitoring for unusual environment variable modifications and unauthorized DLL loading activities should be implemented as part of comprehensive security operations to detect potential exploitation attempts. The vulnerability serves as a reminder of the critical security implications that can arise from seemingly benign system components like time synchronization services that operate with elevated privileges and handle external configuration inputs.