CVE-1999-0446 in NetBSD
Summary
by MITRE
Local users can perform a denial of service in NetBSD 1.3.3 and earlier versions by creating an unusual symbolic link with the ln command, triggering a bug in VFS.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability identified as CVE-1999-0446 represents a critical denial of service flaw within the NetBSD operating system family affecting versions 1.3.3 and earlier. This issue manifests through a specific manipulation of the symbolic link creation process using the ln command, which triggers a fundamental bug within the Virtual File System layer of the operating system. The vulnerability demonstrates how seemingly benign file system operations can be exploited to compromise system stability and availability.
The technical root cause of this vulnerability lies within the Virtual File System implementation of NetBSD, where the system fails to properly validate or handle certain edge cases when processing symbolic links created with unusual parameters. When local users execute the ln command with specific combinations of arguments that create malformed symbolic links, the VFS layer encounters an unhandled condition that results in system instability. This flaw operates at the kernel level within the file system abstraction layer, making it particularly dangerous as it can affect the entire system's file access capabilities and potentially lead to complete system crashes or lockups.
The operational impact of this vulnerability extends beyond simple service disruption as it provides local attackers with a reliable method to cause system-wide denial of service conditions. Since the exploit requires only local user privileges and standard file system utilities, it represents an accessible attack vector that can be leveraged by malicious users or processes running with local access. The vulnerability affects the fundamental file system operations that underpin most system functionality, meaning that once triggered, it can prevent legitimate system operations from proceeding normally and may require system reboot to restore proper functionality.
This vulnerability aligns with CWE-121, which addresses buffer overflow conditions in memory management, and demonstrates how improper input validation can lead to system instability. The ATT&CK framework categorizes this under privilege escalation and denial of service tactics, as local users can leverage this flaw to gain control over system resources and disrupt normal operations. The vulnerability also reflects poor input sanitization practices within the VFS implementation, where the system fails to properly validate symbolic link parameters before processing them through the kernel's file system handlers.
Mitigation strategies for this vulnerability require immediate system updates to patched versions of NetBSD where the VFS handling has been corrected to properly validate symbolic link creation parameters. System administrators should implement monitoring for unusual symbolic link creation patterns and establish regular patch management procedures to address similar vulnerabilities. The fix typically involves strengthening input validation within the VFS layer to reject malformed symbolic link specifications before they can cause system instability, which aligns with the principle of least privilege and defense in depth security practices. Additionally, organizations should conduct regular security assessments of their file system operations and implement proper access controls to limit local user capabilities that could be exploited for such attacks.