CVE-2005-4733 in NetBSD
Summary
by MITRE
NetBSD 2.0 before 20050316 and NetBSD-current before 20050112 allow local users to cause a denial of service (infinite loop and system hang) by calling the F_CLOSEM fcntl with a parameter value of 0.
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Analysis
by VulDB Data Team • 06/08/2017
The vulnerability described in CVE-2005-4733 represents a critical denial of service flaw affecting NetBSD operating systems prior to specific patch releases. This issue manifests when local users execute malicious fcntl system calls with the F_CLOSEM command parameter set to zero value, creating conditions that result in infinite loops and complete system hangs. The vulnerability specifically impacts NetBSD 2.0 releases before 20050316 and NetBSD-current versions before 20050112, indicating a timeframe of vulnerability that spans several months of development cycle. The flaw demonstrates a fundamental error in system call parameter validation and processing logic within the file descriptor management subsystem of the operating system kernel.
The technical root cause of this vulnerability lies in improper handling of the F_CLOSEM fcntl command when invoked with parameter value zero. The F_CLOSEM command is designed to close all file descriptors in a process's file descriptor table that have been marked for closing on exec, but the implementation fails to properly validate the parameter value. When parameter zero is passed, the kernel enters an infinite loop during processing, causing the system to become unresponsive and effectively denying service to legitimate users and processes. This behavior constitutes a classic example of a resource exhaustion attack that does not require elevated privileges but can completely compromise system availability. The flaw operates at the kernel level and affects the core file descriptor management functionality, making it particularly dangerous as it can impact any process attempting to use the fcntl system call with this specific parameter combination.
The operational impact of CVE-2005-4733 extends beyond simple system unavailability to represent a significant threat to system stability and reliability. Local users can exploit this vulnerability without requiring administrative privileges, making it particularly concerning for multi-user systems where unauthorized users might attempt to disrupt system operations. The infinite loop condition causes the kernel to consume 100% CPU resources continuously, preventing legitimate system processes from executing and effectively creating a denial of service condition that can persist until system reboot. This vulnerability directly maps to CWE-835, which describes the weakness of an infinite loop or infinite recursion, and aligns with ATT&CK technique T1499.004 for network denial of service attacks. The flaw can be exploited in various scenarios including web servers, database systems, or any service running on affected NetBSD systems where local users have access to execute shell commands or applications that might invoke the problematic fcntl call.
Mitigation strategies for this vulnerability require immediate system updates to patched versions of NetBSD that address the flawed fcntl implementation. System administrators should prioritize applying the relevant security patches released by NetBSD developers, specifically targeting the versions that include fixes for the F_CLOSEM command handling. Additionally, monitoring systems should be implemented to detect unusual patterns of fcntl system calls or processes consuming excessive CPU resources that might indicate exploitation attempts. Access controls should be reviewed to limit local user privileges where possible, and system hardening measures should be implemented to prevent unauthorized users from executing potentially malicious code. The vulnerability demonstrates the importance of proper parameter validation in kernel space operations and serves as a reminder of the critical nature of thorough testing for system calls that interact with core operating system functionality. Organizations maintaining NetBSD systems should also implement regular security audits and vulnerability assessments to identify similar issues in other system components that might present comparable risks to system availability and stability.