CVE-2000-0456 in NetBSD
Summary
by MITRE
NetBSD 1.4.2 and earlier allows local users to cause a denial of service by repeatedly running certain system calls in the kernel which do not yield the CPU, aka "cpu-hog".
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Analysis
by VulDB Data Team • 04/21/2026
The vulnerability identified as CVE-2000-0456 represents a significant denial of service weakness in NetBSD operating systems version 1.4.2 and earlier. This flaw specifically targets the kernel's handling of certain system calls that do not voluntarily yield the CPU during execution, creating a condition where malicious or unauthorized local users can exploit this behavior to consume excessive system resources. The vulnerability operates within the fundamental architecture of the kernel's scheduling and resource management mechanisms, where specific system calls fail to properly relinquish processor time, leading to system instability and potential complete system lockup.
The technical implementation of this vulnerability stems from the kernel's inability to properly manage CPU cycles when executing certain system calls that are designed to operate in a non-blocking manner. These system calls, when invoked repeatedly by a local user, create a scenario where the CPU becomes trapped in a continuous loop without yielding control to other processes or the scheduler. This behavior directly violates the expected kernel design principles where system calls should either complete their operation and return control to the calling process or voluntarily yield the CPU when waiting for resources. The root cause lies in the kernel's process management and scheduling algorithms that fail to properly handle these specific system call patterns, creating an environment where CPU utilization becomes artificially inflated without proper resource accounting.
The operational impact of this vulnerability extends beyond simple system performance degradation to potentially complete system compromise and denial of service conditions. Local users with minimal privileges can exploit this weakness to exhaust system resources, making the system unresponsive to legitimate user requests and system processes. The vulnerability particularly affects multi-user systems where multiple users might be running processes that inadvertently trigger these problematic system calls, or where malicious users deliberately exploit the vulnerability to disrupt system operations. This type of attack represents a classic example of a resource exhaustion attack that can be particularly devastating in server environments where system availability is critical for business operations.
From a cybersecurity perspective, this vulnerability aligns with several common attack patterns and threat models documented in the cybersecurity community. The flaw demonstrates characteristics consistent with the attack technique described in the MITRE ATT&CK framework under the category of privilege escalation and denial of service attacks. The vulnerability also relates to CWE-400, which describes "Uncontrolled Resource Consumption" and specifically addresses situations where resource exhaustion occurs due to improper handling of system calls or process management. Organizations affected by this vulnerability must implement immediate mitigations including system updates to newer NetBSD versions, kernel parameter tuning to limit resource consumption, and monitoring systems to detect unusual CPU usage patterns that might indicate exploitation attempts.
Mitigation strategies for CVE-2000-0456 primarily focus on system updates and kernel parameter modifications. The most effective approach involves upgrading to NetBSD versions that have addressed this specific kernel scheduling issue through improved resource management and proper CPU yielding mechanisms. System administrators should also implement resource limits and process monitoring to detect and prevent exploitation attempts. Additionally, the vulnerability highlights the importance of proper kernel testing and validation, particularly for system calls that operate in kernel space, to ensure that all processes properly yield CPU control and maintain system stability under various load conditions. The incident underscores the critical need for robust kernel design practices that prevent single points of failure in system resource management and maintain overall system resilience against resource exhaustion attacks.