CVE-2002-0831 in FreeBSD
Summary
by MITRE
The kqueue mechanism in FreeBSD 4.3 through 4.6 STABLE allows local users to cause a denial of service (kernel panic) via a pipe call in which one end is terminated and an EVFILT_WRITE filter is registered for the other end.
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Analysis
by VulDB Data Team • 09/06/2019
The vulnerability described in CVE-2002-0831 represents a critical kernel-level flaw within the FreeBSD operating system's kqueue mechanism. This issue affects FreeBSD versions 4.3 through 4.6 STABLE and demonstrates a classic case of improper resource handling that can lead to system instability. The kqueue facility serves as an event notification interface that allows processes to monitor file descriptors for various events, making it a fundamental component of the system's I/O multiplexing capabilities. When combined with the specific conditions outlined in this vulnerability, the mechanism becomes susceptible to exploitation that can result in complete system crashes.
The technical flaw manifests when a local user executes a specific sequence involving pipe operations and event filtering. The vulnerability occurs during the pipe call process where one end of the pipe is terminated while an EVFILT_WRITE filter is simultaneously registered for the other end. This creates a race condition or improper state management within the kernel's event handling code. The EVFILT_WRITE filter is designed to monitor write events on file descriptors, but when combined with the specific termination scenario of the pipe, it triggers an unexpected code path that leads to kernel memory corruption. This improper handling results in a kernel panic, which is the operating system's response to a critical error that cannot be recovered from, effectively causing a system crash and denial of service for all running processes.
The operational impact of this vulnerability extends beyond simple system availability concerns as it represents a local privilege escalation vector that can be exploited by any user with access to the system. The fact that this vulnerability exists in the kernel level means that exploitation does not require special privileges beyond normal user access, making it particularly dangerous in multi-user environments. System administrators face the challenge of maintaining service availability while dealing with a vulnerability that can be triggered through legitimate system operations. The potential for denial of service attacks is significant, as any local user could potentially crash the entire system, leading to data loss and service interruption. This vulnerability also highlights the importance of thorough testing and code review in kernel-level components, as the interaction between different subsystems can create unexpected behaviors that compromise system stability.
Mitigation strategies for this vulnerability primarily focus on immediate system updates and patches provided by FreeBSD developers. Organizations should prioritize applying the official security patches released by FreeBSD to address the specific kernel code issues that enable this exploit. Additionally, system administrators should consider implementing monitoring solutions that can detect anomalous pipe usage patterns or excessive kqueue operations that might indicate attempted exploitation. The vulnerability also underscores the importance of following secure coding practices and conducting thorough testing of kernel components, particularly those involving event notification mechanisms and resource management. From a defense-in-depth perspective, limiting local user access where possible and implementing proper system hardening measures can reduce the attack surface. This vulnerability aligns with CWE-119, which addresses memory corruption issues, and can be mapped to ATT&CK technique T1499.004, which covers system shutdown/reboot attacks, as the exploitation results in system-wide denial of service through kernel panic conditions.