CVE-2005-2134 in NetBSD
Summary
by MITRE
The (1) clcs and (2) emuxki drivers in NetBSD 1.6 through 2.0.2 allow local users to cause a denial of service (kernel crash) by using the set-parameters ioctl on an audio device to change the block size and set the pause state to "unpaused" in the same ioctl, which causes a divide-by-zero error.
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Analysis
by VulDB Data Team • 07/03/2019
The vulnerability described in CVE-2005-2134 represents a critical kernel-level flaw affecting the clcs and emuxki audio drivers in NetBSD versions 1.6 through 2.0.2. This issue manifests as a denial of service condition that can result in complete system kernel crashes, fundamentally compromising the stability and availability of affected systems. The vulnerability specifically targets the audio subsystem drivers that handle audio device parameter configuration through ioctl system calls, making it particularly dangerous in environments where audio functionality is critical to system operations.
The technical root cause of this vulnerability lies in improper input validation within the ioctl handling mechanisms of the affected audio drivers. When a local user executes a specific sequence of operations using the set-parameters ioctl on audio devices, the system processes two distinct parameters simultaneously: block size modification and pause state configuration. The flaw occurs when the pause state is explicitly set to "unpaused" while simultaneously altering the block size parameter. This particular combination triggers a divide-by-zero error within the kernel code, as the system attempts to perform mathematical operations on invalid or zero values derived from the manipulated parameters. The divide-by-zero condition causes the kernel to crash and terminate the audio driver subsystem, resulting in a complete system hang or reboot.
From an operational perspective, this vulnerability presents significant risks for system administrators and security professionals managing NetBSD-based systems. The local privilege requirement means that an attacker must already have access to the system to exploit this vulnerability, but the potential for system-wide disruption remains high since audio device access is often available to regular users. The impact extends beyond simple service interruption, as kernel crashes can lead to data loss, system instability, and potential denial of service for other critical system functions. The vulnerability affects systems where audio functionality is actively used, making it particularly concerning for servers, workstations, and embedded systems that rely on audio processing capabilities.
The vulnerability maps directly to CWE-369, which identifies "Divide by Zero" as a critical weakness in software systems. This classification emphasizes the fundamental nature of the flaw, where mathematical operations are performed without proper validation of divisor values. Additionally, the vulnerability aligns with ATT&CK technique T1499.001, which describes "Network Denial of Service" through kernel-level manipulation, though in this case the attack vector is local rather than network-based. The attack requires minimal privileges and sophisticated understanding of the audio driver interfaces, making it a particularly insidious threat that can be exploited by both malicious insiders and determined external attackers who have gained local access to the system.
Mitigation strategies for this vulnerability should prioritize immediate system updates and patches provided by NetBSD security teams. System administrators should implement strict access controls to audio devices and monitor for unauthorized ioctl operations on audio subsystems. The recommended approach involves applying the official security patches released by NetBSD that correct the input validation issues within the clcs and emuxki drivers. Additional protective measures include implementing kernel hardening techniques such as enabling kernel address space layout randomization and restricting user access to audio device interfaces through proper permission controls. Regular security audits should verify that audio driver configurations do not expose unnecessary functionality to untrusted users, and system monitoring should be enhanced to detect unusual ioctl activity patterns that might indicate exploitation attempts. Organizations should also consider implementing intrusion detection systems that can identify and alert on suspicious audio device parameter changes that could precede kernel crashes.