CVE-2015-7849 in ntpd
Summary
by MITRE
Use-after-free vulnerability in ntpd in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows remote authenticated users to possibly execute arbitrary code or cause a denial of service (crash) via crafted packets.
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Analysis
by VulDB Data Team • 06/24/2022
The CVE-2015-7849 vulnerability represents a critical use-after-free flaw in the Network Time Protocol daemon ntpd that affected versions of NTP software prior to 4.2.8p4 and 4.3.77. This vulnerability resides within the time synchronization service that millions of devices rely upon for accurate timekeeping across global networks. The flaw manifests when the ntpd daemon processes malformed or specially crafted network packets, creating a scenario where memory previously allocated to a data structure is accessed after it has been freed, leading to unpredictable behavior and potential exploitation.
The technical nature of this vulnerability stems from improper memory management within the ntpd application's packet processing routines. When authenticated remote attackers send specifically crafted packets to an affected NTP server, the daemon fails to properly validate or handle these inputs, resulting in a use-after-free condition. This memory corruption vulnerability can be exploited to execute arbitrary code with the privileges of the ntpd process, potentially allowing attackers to gain full control over the affected system. The vulnerability is particularly dangerous because it requires only authenticated access, meaning that an attacker who can establish a session with the NTP service can trigger the flaw.
The operational impact of CVE-2015-7849 extends beyond simple denial of service scenarios to encompass full system compromise and persistent backdoor access. Organizations relying on NTP for time synchronization across their infrastructure face significant risk as attackers can leverage this vulnerability to establish persistent presence within their networks. The vulnerability affects not only individual servers but also entire network time synchronization hierarchies, potentially allowing attackers to disrupt time services across multiple systems simultaneously. This makes it particularly concerning for critical infrastructure environments where time synchronization is essential for security logging, audit trails, and coordinated system operations.
Mitigation strategies for CVE-2015-7849 focus primarily on immediate software updates to patched versions of NTP software, which address the underlying memory management issues in the ntpd daemon. System administrators should prioritize patching all affected NTP servers and implement network segmentation to limit exposure to untrusted networks. Additional defensive measures include implementing strict access controls for NTP services, monitoring for unusual packet patterns, and deploying intrusion detection systems that can identify exploitation attempts. The vulnerability aligns with CWE-416, which addresses use-after-free conditions, and represents a classic example of memory safety issues that can lead to privilege escalation according to ATT&CK framework techniques for privilege escalation through memory corruption. Organizations should also consider implementing network access controls that limit NTP service exposure to only trusted hosts and establish robust monitoring for time synchronization anomalies that might indicate exploitation attempts.