CVE-2001-1559 in OpenBSD
Summary
by MITRE
The uipc system calls (uipc_syscalls.c) in OpenBSD 2.9 and 3.0 provide user mode return instead of versus rval kernel mode values to the fdrelease function, which allows local users to cause a denial of service and trigger a null dereference.
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Analysis
by VulDB Data Team • 12/25/2024
The vulnerability described in CVE-2001-1559 represents a critical kernel-level flaw within the OpenBSD operating system's user interface protocol control (uipc) subsystem. This issue affects versions 2.9 and 3.0 of the OpenBSD kernel, where the uipc system calls are implemented in the uipc_syscalls.c source file. The flaw manifests in the improper handling of return values during the fdrelease function execution, creating a scenario where user-mode processes can manipulate kernel behavior through crafted system call sequences.
The technical root cause of this vulnerability stems from a fundamental error in kernel memory management and return value handling within the uipc subsystem. When the fdrelease function is invoked through uipc system calls, the kernel incorrectly returns user-mode values instead of the expected kernel-mode rval values. This mismanagement creates a condition where a local attacker can craft specific input parameters that trigger a null pointer dereference during the function execution. The null dereference occurs because the kernel attempts to access memory at address zero, which is not mapped in the kernel's virtual address space, leading to immediate system termination or kernel panic.
From an operational perspective, this vulnerability presents a significant denial of service risk that can be exploited by any local user with access to the system. The impact extends beyond simple service disruption as the null dereference can cause complete system crashes, requiring manual reboot to restore normal operation. The vulnerability is particularly dangerous in multi-user environments where unprivileged users could potentially destabilize the entire system. Additionally, the nature of kernel-level flaws means that exploitation could potentially lead to privilege escalation or other secondary effects, though the primary impact documented is denial of service.
The vulnerability aligns with CWE-476, which describes null pointer dereference conditions in software systems, and demonstrates poor input validation and memory management practices within kernel space. From an attack framework perspective, this issue maps to the technique of kernel exploitation through system call manipulation, which is categorized under the ATT&CK framework's privilege escalation and defense evasion tactics. The attack surface is limited to local users who can execute system calls, but the impact is severe due to the kernel-level nature of the flaw.
Mitigation strategies for CVE-2001-1559 primarily involve upgrading to patched versions of OpenBSD, specifically versions beyond 3.0 where the kernel code has been corrected to properly handle return values in the fdrelease function. System administrators should also implement proper access controls to limit local user privileges where possible, and monitor for unusual system behavior that might indicate exploitation attempts. The fix requires careful attention to ensure that kernel return value handling is properly maintained throughout the uipc subsystem, preventing the erroneous user-mode value return that triggers the null pointer dereference condition. Additionally, regular security audits of kernel code should be conducted to identify similar memory management issues that could create comparable vulnerabilities in other subsystems.