CVE-1999-0747 in BSD OS
Summary
by MITRE
Denial of service in BSDi Symmetric Multiprocessing (SMP) when an fstat call is made when the system has a high CPU load.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability described in CVE-1999-0747 represents a critical denial of service condition affecting BSDi Symmetric Multiprocessing systems during high CPU load scenarios. This issue specifically manifests when the fstat system call is executed under conditions of elevated system processing demands, creating a scenario where legitimate system operations can be disrupted through careful exploitation of the kernel's handling of file status information requests.
The technical flaw resides in the kernel's implementation of the fstat system call within the SMP framework of BSDi operating systems. When the system experiences high CPU utilization, the kernel's internal mechanisms for processing file status requests become susceptible to resource exhaustion or deadlock conditions. The vulnerability exploits the interaction between the multiprocessing scheduler and the file system subsystem, where concurrent access to file metadata structures during peak processing loads causes the kernel to enter an unstable state that ultimately results in system unresponsiveness or complete system crash.
This vulnerability impacts the operational integrity of BSDi systems by creating a condition where legitimate user processes and system services can be rendered unavailable through a simple file status inquiry operation. The denial of service occurs because the kernel's response to fstat calls becomes increasingly unpredictable under load, potentially leading to system hangs, process termination, or complete system failure. The vulnerability is particularly concerning in production environments where system stability and availability are paramount, as it can be triggered by routine system operations without requiring elevated privileges or specialized knowledge.
The operational impact extends beyond simple system unavailability to encompass potential data integrity concerns and service disruption in mission-critical applications. Organizations running BSDi systems may experience unexpected downtime or performance degradation when the system encounters high processing loads, particularly in environments where file operations are frequent or where automated processes perform regular status checks. The vulnerability demonstrates a fundamental flaw in kernel design where resource management under concurrent load conditions fails to properly handle standard system calls.
Mitigation strategies for this vulnerability should focus on implementing proper kernel resource management and load handling mechanisms. System administrators should consider implementing CPU load monitoring and limiting file system operations during peak processing times. The recommended approach involves updating to patched kernel versions that address the specific race conditions and resource management issues within the fstat implementation. Additionally, implementing proper system load balancing and avoiding conditions that lead to sustained high CPU utilization can help prevent exploitation of this vulnerability. Organizations should also consider implementing monitoring solutions that can detect and alert on unusual system behavior patterns that may indicate attempted exploitation of this denial of service condition. This vulnerability aligns with CWE-362, which addresses race conditions in kernel operations, and represents a classic example of how system design flaws can create exploitable conditions under specific load scenarios.