CVE-2016-2518 in ntp
Summary
by MITRE
The MATCH_ASSOC function in NTP before version 4.2.8p9 and 4.3.x before 4.3.92 allows remote attackers to cause an out-of-bounds reference via an addpeer request with a large hmode value.
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Analysis
by VulDB Data Team • 07/27/2022
The vulnerability identified as CVE-2016-2518 represents a critical out-of-bounds memory access flaw within the Network Time Protocol implementation, specifically affecting the MATCH_ASSOC function in NTP versions prior to 4.2.8p9 and 4.3.x versions before 4.3.92. This issue arises from insufficient input validation when processing addpeer requests, creating a scenario where remote attackers can exploit the protocol's handling of the hmode parameter to trigger memory corruption. The vulnerability falls under the category of buffer overflow conditions as classified by CWE-129, specifically manifesting as an out-of-bounds read operation that can lead to arbitrary code execution or system instability.
The technical implementation of this vulnerability exploits the lack of proper bounds checking in the MATCH_ASSOC function which processes peer association requests. When an attacker sends an addpeer request containing an excessively large hmode value, the function fails to validate the parameter against expected ranges, allowing the code to attempt memory access beyond allocated boundaries. This flaw operates at the protocol level where NTP servers process peer configuration requests, making it particularly dangerous as it can be exploited without authentication. The vulnerability is classified as a remote code execution vector under the ATT&CK framework with techniques categorized under T1210 - Exploitation of Remote Services and T1059 - Command and Scripting Interpreter, as it enables attackers to manipulate the NTP daemon's memory state.
The operational impact of CVE-2016-2518 extends beyond simple service disruption, as successful exploitation can result in complete system compromise of time synchronization services. Network time protocol servers are fundamental infrastructure components that many systems depend upon for accurate timekeeping, authentication, and logging. When compromised, these servers can provide attackers with a persistent foothold for further network infiltration or enable time-based attacks that bypass security controls. The vulnerability affects systems where NTP is used for peer synchronization, including critical infrastructure components such as network switches, routers, servers, and security appliances that rely on accurate time synchronization for proper operation. The flaw can also contribute to denial of service conditions that disrupt time synchronization across entire networks, as affected systems may crash or become unresponsive.
Mitigation strategies for CVE-2016-2518 should prioritize immediate patching of affected NTP implementations to versions 4.2.8p9 or 4.3.92 and later, which contain the necessary input validation fixes. Network administrators should implement access controls that restrict peer configuration requests to trusted sources only, utilizing firewall rules and NTP access control lists to limit exposure. Additionally, monitoring systems should be configured to detect unusual addpeer request patterns or hmode parameter values that may indicate exploitation attempts. The implementation of intrusion detection systems with signature-based detection for this specific vulnerability pattern can provide early warning of potential attacks. Organizations should also consider implementing network segmentation to isolate critical time synchronization services and employ regular vulnerability assessments to identify other potential entry points that could be combined with this vulnerability for more sophisticated attacks.