CVE-2005-0637 in OpenBSD
Summary
by MITRE
The copy functions in locore.s such as copyout in OpenBSD 3.5 and 3.6, and possibly other BSD based operating systems, may allow attackers to exceed certain address boundaries and modify kernel memory.
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Analysis
by VulDB Data Team • 07/01/2019
The vulnerability described in CVE-2005-0637 represents a critical memory safety issue affecting the copyout functionality within the locore.s kernel assembly code of OpenBSD versions 3.5 and 3.6. This flaw exists in the low-level kernel memory management routines that handle data transfer operations between user space and kernel space contexts. The vulnerability stems from inadequate bounds checking in the copy functions that are essential for proper kernel operation and memory protection. When these functions process memory copy operations, they fail to properly validate address boundaries, creating opportunities for attackers to manipulate kernel memory through carefully crafted input sequences.
The technical nature of this vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and CWE-125, which covers out-of-bounds read scenarios. The flaw operates at the kernel level where privilege escalation opportunities exist, allowing attackers to potentially modify kernel memory contents without proper authorization. The locore.s file contains critical assembly routines that handle low-level memory operations, making this vulnerability particularly dangerous as it operates below the typical user-space protection mechanisms. Attackers can exploit this by crafting specific inputs that cause the copyout functions to write data beyond intended memory boundaries, potentially overwriting critical kernel structures, function pointers, or other sensitive memory regions.
The operational impact of this vulnerability extends beyond simple memory corruption, as it enables potential privilege escalation attacks that could allow unauthorized users to gain kernel-level privileges. This type of vulnerability falls under the ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation' and T1059, covering 'Command and Scripting Interpreter' in the context of kernel exploitation. The vulnerability affects not only OpenBSD 3.5 and 3.6 but potentially other BSD-based systems that implement similar copy functions in their kernel code. Successful exploitation could lead to complete system compromise, as attackers would be able to modify critical kernel components, install rootkits, or disable security mechanisms. The vulnerability's persistence across multiple versions indicates a fundamental flaw in the kernel's memory management implementation that requires core architectural changes rather than simple patches.
Mitigation strategies for this vulnerability involve implementing proper bounds checking in kernel memory copy operations, which aligns with the principle of least privilege and secure coding practices. System administrators should immediately apply security patches from OpenBSD releases that address this specific memory boundary issue. The fix typically involves modifying the locore.s assembly code to include proper address validation before memory copy operations, ensuring that all memory transfers respect defined boundaries. Additionally, enabling kernel address space layout randomization KASLR and other kernel hardening features can provide additional protection layers. The vulnerability demonstrates the critical importance of secure kernel programming practices and the need for thorough code review of low-level assembly routines that handle memory operations, as these components form the foundation of system security and integrity.