CVE-2000-0461 in FreeBSD
Summary
by MITRE
The undocumented semconfig system call in BSD freezes the state of semaphores, which allows local users to cause a denial of service of the semaphore system by using the semconfig call.
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Analysis
by VulDB Data Team • 04/21/2026
The vulnerability described in CVE-2000-0461 represents a critical flaw in the Berkeley Software Distribution operating system family that affects the semaphore management subsystem. This issue stems from an undocumented system call named semconfig which was designed to control the internal state of semaphores within the system. The semconfig system call, while functional, was not properly documented in the standard system call interfaces, creating a situation where developers and system administrators were unaware of its existence and potential impact on system stability. The vulnerability occurs when local users exploit this undocumented interface to freeze the state of semaphores, effectively causing the entire semaphore system to become unresponsive and leading to a denial of service condition. This type of vulnerability falls under the category of improper handling of system calls and demonstrates how undocumented features can create security risks that are difficult to detect and mitigate.
The technical implementation of this vulnerability involves the manipulation of semaphore state through the semconfig system call, which operates at a low level within the kernel space of the operating system. When invoked improperly, this system call can cause semaphores to enter an inconsistent state where they remain frozen indefinitely, preventing other processes from acquiring or releasing semaphore locks. This behavior effectively blocks all semaphore operations within the system, creating a cascading failure that can affect multiple applications and system services that depend on proper semaphore functionality. The flaw demonstrates a lack of proper input validation and state management within the kernel's semaphore subsystem, as the system does not adequately protect against malicious or accidental invocation of this undocumented interface. From a cybersecurity perspective, this vulnerability represents a classic example of how undocumented system interfaces can create attack vectors that are not covered by standard security controls or monitoring systems.
The operational impact of this vulnerability extends beyond simple denial of service, as it can compromise the stability and reliability of systems that rely heavily on inter-process communication through semaphores. Local users with access to the system can exploit this weakness to disrupt critical services, potentially causing system-wide instability and requiring manual intervention to restore normal operation. The freeze state of semaphores can persist until the system is rebooted, making this a particularly disruptive attack vector that can be used to effectively disable system functionality. This vulnerability has implications for system administrators who may not be aware of the existence of the semconfig system call, as it represents a hidden attack surface that is not typically monitored or protected by standard security measures. The impact is particularly severe in multi-user environments where local privilege escalation or unauthorized access to system resources could be leveraged to trigger this denial of service condition.
Mitigation strategies for CVE-2000-0461 should focus on both immediate system hardening and long-term architectural improvements. The most effective immediate solution involves removing or disabling the undocumented semconfig system call from the system, which requires careful analysis of system dependencies to ensure no legitimate applications rely on this interface. System administrators should implement comprehensive monitoring of system calls and kernel activity to detect unauthorized invocation of undocumented interfaces, which aligns with the principles of the ATT&CK framework under the system interaction category. Additionally, regular security audits and code reviews should be conducted to identify other undocumented system features that may present similar vulnerabilities. The vulnerability highlights the importance of proper system call documentation and access control mechanisms, as recommended by various cybersecurity standards including those related to secure coding practices and kernel security. Organizations should also implement proper privilege management and access controls to limit local user capabilities that could lead to exploitation of such vulnerabilities, as outlined in the CWE classification for improper handling of system calls and inadequate input validation.