CVE-1999-1314 in FreeBSD
Summary
by MITRE
Vulnerability in union file system in FreeBSD 2.2 and earlier, and possibly other operating systems, allows local users to cause a denial of service (system reload) via a series of certain mount_union commands.
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Analysis
by VulDB Data Team • 04/16/2026
The vulnerability described in CVE-1999-1314 resides within the union file system implementation of FreeBSD versions 2.2 and earlier, representing a significant security flaw that affects system stability and availability. This issue specifically targets the union file system mechanism that allows users to overlay multiple directory trees, creating a single unified view of the filesystem structure. The vulnerability manifests when local users execute a sequence of carefully crafted mount_union commands that exploit a flaw in the kernel's handling of union filesystem operations.
The technical flaw stems from inadequate input validation and error handling within the union filesystem driver. When users issue multiple mount_union commands in succession, the system fails to properly manage the internal data structures associated with union mounts, leading to memory corruption or resource exhaustion conditions. This particular vulnerability falls under the category of improper handling of system resources, which is classified as CWE-399 in the Common Weakness Enumeration framework. The flaw does not require elevated privileges to exploit, making it particularly dangerous as any local user can potentially trigger the condition.
The operational impact of this vulnerability extends beyond simple system instability, as it can force complete system reloads or reboot cycles, effectively creating a denial of service condition that affects legitimate users and services. In environments where FreeBSD systems serve critical functions, such as network servers or file storage systems, this vulnerability could result in significant downtime and service disruption. The system reload required to recover from this condition represents a substantial operational cost, as it interrupts ongoing processes and may lead to data loss or inconsistency in applications that were running during the incident.
From an attacker's perspective, this vulnerability aligns with techniques documented in the MITRE ATT&CK framework under the T1499 category of Network Denial of Service, as it enables local users to disrupt system availability through kernel-level manipulation. The exploitation process involves crafting specific sequences of mount_union commands that stress the filesystem driver beyond its intended operational parameters, ultimately causing the kernel to become unstable and requiring system restart to restore normal operation. Organizations should note that this vulnerability represents a fundamental flaw in kernel memory management and resource allocation that affects the core operating system functionality.
Mitigation strategies for CVE-1999-1314 primarily focus on immediate system updates and patches provided by FreeBSD developers, as the vulnerability existed in versions prior to 2.2.2. System administrators should implement strict access controls and monitor for unusual mount_union command usage patterns that might indicate exploitation attempts. Additionally, organizations should consider implementing kernel security modules or extended monitoring solutions that can detect anomalous filesystem behavior and alert administrators to potential exploitation attempts. The vulnerability also underscores the importance of proper kernel testing and validation before deployment, as it represents a failure in the quality assurance process that allowed such a fundamental flaw to persist in released software versions.