CVE-2001-0268 in NetBSD
Summary
by MITRE
The i386_set_ldt system call in NetBSD 1.5 and earlier, and OpenBSD 2.8 and earlier, when the USER_LDT kernel option is enabled, does not validate a call gate target, which allows local users to gain root privileges by creating a segment call gate in the Local Descriptor Table (LDT) with a target that specifies an arbitrary kernel address.
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Analysis
by VulDB Data Team • 12/14/2024
The vulnerability described in CVE-2001-0268 represents a critical privilege escalation flaw in the kernel-level memory management subsystem of several Unix-like operating systems. This issue affects NetBSD versions 1.5 and earlier, as well as OpenBSD versions 2.8 and earlier, specifically when the USER_LDT kernel option is enabled. The vulnerability stems from insufficient validation mechanisms within the i386_set_ldt system call, which is responsible for managing the Local Descriptor Table (LDT) in x86 architectures. The LDT serves as a per-process descriptor table that contains segment descriptors for code and data segments, making it a critical component in the memory protection and privilege management architecture of these operating systems.
The technical flaw manifests in the improper validation of call gate targets within the Local Descriptor Table. A call gate is a special type of segment descriptor that defines a procedure entry point and contains a target address that specifies where a procedure should execute. When the USER_LDT option is enabled, users can manipulate the LDT through the i386_set_ldt system call, but the kernel fails to validate that the target address specified in a call gate points to a legitimate kernel address. This validation gap allows a local attacker to construct a malicious segment call gate with a target address pointing to arbitrary kernel memory locations, effectively bypassing the normal privilege boundaries that separate user space from kernel space.
The operational impact of this vulnerability is severe as it enables local users to achieve root privilege escalation without requiring any special privileges or external exploitation vectors. Once an attacker successfully creates a malicious call gate with a kernel target address, they can execute arbitrary code with kernel-level privileges, potentially leading to complete system compromise. This vulnerability directly violates the fundamental security principle of privilege separation and allows attackers to bypass kernel memory protection mechanisms, including those designed to prevent user processes from accessing kernel memory directly. The attack requires only local access to the system, making it particularly dangerous as it can be exploited by any user with login credentials, regardless of their initial privilege level.
The vulnerability aligns with CWE-119, which addresses improper restriction of operations within a memory buffer, and represents a classic case of insufficient input validation in kernel space. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques, specifically the use of kernel exploits to gain elevated privileges. The attack vector follows the pattern of local privilege escalation through kernel memory corruption or manipulation, where the attacker leverages a flaw in the kernel's descriptor table management to execute code with the highest system privileges. The vulnerability demonstrates the critical importance of proper kernel validation mechanisms and highlights the risks associated with allowing user-space processes to manipulate low-level kernel data structures without adequate safeguards.
Mitigation strategies for this vulnerability include disabling the USER_LDT kernel option when it is not required, updating to patched versions of the affected operating systems, and implementing proper kernel memory protection mechanisms. System administrators should also consider implementing additional security controls such as mandatory access controls, kernel hardening measures, and monitoring for suspicious LDT manipulation attempts. The vulnerability underscores the necessity of thorough kernel code review processes, particularly for system calls that handle low-level memory management operations, and emphasizes the importance of maintaining up-to-date security patches in production environments. Regular security assessments of kernel configurations and access controls should be conducted to prevent similar vulnerabilities from being exploited in the future.