CVE-1999-0323 in FreeBSD
Summary
by MITRE
freebsd mmap function allows users to modify append-only or immutable files.
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Analysis
by VulDB Data Team • 04/17/2026
The vulnerability described in CVE-1999-0323 represents a critical security flaw in the FreeBSD operating system's memory mapping implementation that directly undermines file system integrity controls. This issue affects the mmap system call functionality which is designed to map files or devices into memory for efficient access. The flaw specifically permits unauthorized modification of files that have been explicitly marked as append-only or immutable, thereby bypassing fundamental file system security mechanisms that should prevent such alterations.
The technical root cause of this vulnerability lies in the improper implementation of access control checks within the FreeBSD kernel's memory mapping subsystem. When users invoke the mmap function on files with append-only or immutable attributes, the system fails to properly validate whether the mapping operation should be permitted based on the file's security properties. This implementation flaw creates a direct pathway for privilege escalation and data integrity compromise, as malicious actors can circumvent the intended protection mechanisms that are typically enforced by the file system to prevent unauthorized modifications to critical system files or user data.
From an operational perspective, this vulnerability poses significant risks to system security and data integrity across FreeBSD environments. The ability to modify append-only or immutable files undermines the fundamental security model that relies on these attributes to protect critical system components, configuration files, and sensitive user data. Attackers can exploit this weakness to maintain persistence, modify system binaries, or corrupt important data files that should remain protected from unauthorized alterations. The impact extends beyond simple file corruption as it effectively neutralizes the security controls that administrators rely upon to maintain system integrity and prevent malicious modifications.
The vulnerability aligns with CWE-284, which addresses improper access control in software systems, and demonstrates how kernel-level implementation flaws can create severe security weaknesses. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and persistence, as adversaries can leverage the ability to modify protected files to establish long-term access to compromised systems. The flaw represents a critical failure in the principle of least privilege and demonstrates how insufficient validation of system calls can undermine the security architecture of operating systems. Organizations running FreeBSD systems are particularly vulnerable to exploitation of this weakness, as it provides a direct mechanism for bypassing file system protections that are essential for maintaining system security and data integrity.
Mitigation strategies should focus on immediate patching of affected FreeBSD versions, implementing additional monitoring for unauthorized file modifications, and reviewing system configurations to minimize the impact of potential exploitation. System administrators should also consider implementing additional security controls such as mandatory access controls or enhanced file integrity monitoring to detect and prevent unauthorized modifications to critical system files. The vulnerability underscores the importance of thorough security testing of kernel-level functions and the critical need for proper access control validation in system call implementations.