CVE-2016-6301 in BusyBox
Summary
by MITRE
The recv_and_process_client_pkt function in networking/ntpd.c in busybox allows remote attackers to cause a denial of service (CPU and bandwidth consumption) via a forged NTP packet, which triggers a communication loop.
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Analysis
by VulDB Data Team • 12/04/2025
The vulnerability identified as CVE-2016-6301 resides within the busybox implementation of the Network Time Protocol daemon, specifically in the recv_and_process_client_pkt function located in networking/ntpd.c. This flaw represents a classic example of a resource exhaustion attack that can be exploited by remote adversaries to disrupt network services. The vulnerability stems from insufficient validation of incoming NTP packets, allowing malicious actors to craft forged packets that trigger unintended behavioral patterns within the NTP daemon. The affected component is part of busybox, a widely deployed collection of common Unix utilities that serves as a foundation for numerous embedded systems and lightweight Linux environments. When a specially crafted NTP packet is received, the function fails to properly validate packet authenticity or integrity, leading to a condition where the daemon enters an infinite processing loop.
The technical execution of this vulnerability involves the manipulation of NTP packet headers and content to exploit the packet processing logic within busybox's ntpd implementation. Attackers can forge NTP packets with specific characteristics that cause the recv_and_process_client_pkt function to continuously process the same packet or enter a loop where it repeatedly handles malformed data. This results in sustained high CPU utilization and continuous network bandwidth consumption as the daemon becomes trapped in an inefficient processing cycle. The communication loop occurs because the function does not properly validate packet sequence numbers, packet types, or other critical NTP protocol elements that would normally prevent such processing anomalies. The flaw demonstrates poor input validation practices and highlights the importance of robust packet filtering mechanisms in network protocol implementations.
The operational impact of this vulnerability extends beyond simple denial of service to potentially compromise entire network infrastructure, particularly in environments where NTP services are critical for time synchronization. Systems running vulnerable versions of busybox may experience complete service unavailability, as the daemon consumes excessive computational resources and network bandwidth. This can affect not only the targeted device but also impact network performance for other services running on the same infrastructure. The vulnerability is particularly concerning in embedded systems, IoT devices, and network appliances that rely on busybox implementations for basic network services. Organizations may experience cascading failures if multiple devices in a network are simultaneously affected, leading to widespread disruption of time-critical operations. The resource consumption patterns make this attack difficult to detect through conventional monitoring as it appears as legitimate network traffic consuming normal processing resources.
Mitigation strategies for CVE-2016-6301 should focus on immediate patching of vulnerable busybox versions and implementation of network-level protections. System administrators should upgrade to patched versions of busybox that contain proper input validation for NTP packets, typically those released after the vulnerability disclosure. Network administrators can implement packet filtering rules at firewalls or network access control points to limit NTP traffic or drop packets from suspicious sources. The implementation of NTP authentication mechanisms and the use of trusted time sources can reduce the attack surface for such exploits. Additionally, monitoring for unusual CPU and bandwidth consumption patterns in NTP services should be implemented as part of security operations. From a cybersecurity perspective, this vulnerability aligns with CWE-248 Uncaught Exception and ATT&CK technique T1499.001 for Network Denial of Service, demonstrating how protocol-level flaws can be exploited for resource exhaustion attacks. Organizations should also consider implementing intrusion detection systems that can identify patterns of NTP packet flooding or abnormal processing behavior that may indicate exploitation attempts.