CVE-2002-1667 in FreeBSD
Summary
by MITRE
The virtual memory management system in FreeBSD 4.5-RELEASE and earlier does not properly check the existence of a VM object during page invalidation, which allows local users to cause a denial of service (crash) by calling msync on an unaccessed memory map created with MAP_ANON and MAP_NOSYNC flags.
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Analysis
by VulDB Data Team • 09/06/2019
The vulnerability described in CVE-2002-1667 represents a critical flaw in the virtual memory management subsystem of FreeBSD operating systems version 4.5-RELEASE and earlier. This issue stems from insufficient validation mechanisms within the kernel's memory management code that handles page invalidation operations. The flaw specifically manifests when the system processes memory synchronization requests on anonymous memory mappings that have been created with particular flag combinations, creating a scenario where the kernel fails to properly verify the existence of virtual memory objects before attempting to invalidate pages.
The technical implementation of this vulnerability exploits a race condition or logic flaw in the memory management subsystem where the kernel does not adequately validate whether a VM object reference is still valid before proceeding with page invalidation procedures. When a local user process creates a memory mapping using the MAP_ANON and MAP_NOSYNC flags, it establishes an anonymous memory region that should be handled differently from regular file-backed mappings. However, the kernel's page invalidation routine fails to properly check for the existence of the underlying VM object, leading to potential null pointer dereferences or invalid memory access patterns that cause the kernel to crash.
This vulnerability presents significant operational impact for FreeBSD systems, particularly in environments where multiple processes might be creating anonymous memory mappings and subsequently invoking msync operations. The local privilege escalation aspect allows any user to potentially crash the entire system, resulting in denial of service conditions that can affect all running services and applications. The crash occurs at the kernel level, meaning that even if individual processes are affected, the broader system stability is compromised, potentially requiring system reboot to restore normal operations.
From a cybersecurity perspective, this vulnerability aligns with CWE-119 which addresses improper access to memory and CWE-476 which covers null pointer dereference conditions. The attack pattern corresponds to privilege escalation techniques within the ATT&CK framework under the T1068 privilege escalation tactic, specifically targeting kernel-level vulnerabilities to achieve system compromise. The exploit requires local access and knowledge of specific memory mapping flags, making it less likely to be exploited remotely but still represents a serious threat to system stability and availability.
Mitigation strategies for this vulnerability include immediate upgrading to FreeBSD versions 4.6-RELEASE or later where the memory management subsystem has been corrected to properly validate VM object existence before page invalidation operations. System administrators should also implement monitoring solutions to detect unusual msync behavior patterns and consider restricting anonymous memory mapping capabilities where possible. Additionally, regular security audits of kernel memory management code should be conducted to identify similar validation gaps that might exist in other system components, ensuring comprehensive protection against similar vulnerabilities in the future.