CVE-1999-0304 in FreeBSD
Summary
by MITRE
mmap function in bsd allows local attackers in the kmem group to modify memory through devices.
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Analysis
by VulDB Data Team • 04/17/2026
The vulnerability described in CVE-1999-0304 represents a critical privilege escalation flaw within the memory management subsystem of BSD operating systems. This issue specifically targets the mmap function implementation and exploits a weakness that allows local attackers who belong to the kmem group to manipulate memory mappings through device interfaces. The vulnerability stems from insufficient access controls and validation mechanisms within the kernel's memory management functions, creating an avenue for unauthorized memory modification that bypasses normal security boundaries.
The technical flaw manifests in the improper handling of memory mapping operations when devices are accessed through the kmem group permissions. The mmap function in BSD systems fails to adequately verify the privileges of processes attempting to modify memory mappings through device interfaces, particularly when these operations involve kernel memory regions. This weakness creates a direct path for local attackers to manipulate memory contents, potentially leading to arbitrary code execution or system compromise. The vulnerability operates at the kernel level, making it particularly dangerous as it can be exploited to bypass user-space protections and directly manipulate kernel data structures.
From an operational impact perspective, this vulnerability severely undermines system security by allowing local users with minimal privileges to gain elevated access to kernel memory spaces. Attackers can leverage this flaw to modify critical kernel data structures, inject malicious code into kernel memory, or manipulate system behavior in ways that would normally require root privileges. The implications extend beyond simple privilege escalation as the ability to modify memory through device interfaces can lead to complete system compromise, data corruption, or denial of service conditions. This vulnerability particularly affects systems where the kmem group has been granted access to device interfaces, making it a significant concern for multi-user environments.
The vulnerability aligns with CWE-264, which addresses permissions, privileges, and access controls in kernel-level operations, and maps to ATT&CK technique T1068, which covers local privilege escalation through kernel exploits. Effective mitigations include implementing stricter access controls for the kmem group, disabling unnecessary device interfaces that allow memory mapping, and applying kernel patches that properly validate memory mapping operations. System administrators should also consider implementing mandatory access controls, monitoring for suspicious memory mapping activities, and ensuring that only trusted users have membership in the kmem group. Regular security audits of kernel memory management functions and device driver interfaces are essential to prevent exploitation of similar vulnerabilities in the future.