CVE-2006-6655 in NetBSD
Summary
by MITRE
The procfs implementation in NetBSD-current before 20061023, NetBSD 3.0 and 3.0.1 before 20061024, and NetBSD 2.x before 20061029 allows local users to cause a denial of service (kernel panic) by attempting to access /emul/linux/proc/0/stat on a procfs filesystem that was mounted with mount_procfs -o linux, which results in a NULL pointer dereference.
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Analysis
by VulDB Data Team • 08/12/2018
The vulnerability described in CVE-2006-6655 represents a critical kernel-level flaw in the NetBSD operating system's implementation of the procfs filesystem. This issue specifically affects systems running NetBSD versions prior to the mentioned patch dates, where the procfs filesystem is mounted with the linux compatibility option. The vulnerability arises from inadequate input validation and memory management within the kernel's procfs subsystem, creating a condition that can be exploited by local users to trigger system-wide crashes. The flaw manifests when attempting to access a specific file path within the linux compatibility layer, making it particularly dangerous in environments where such compatibility features are enabled.
The technical root cause of this vulnerability is a NULL pointer dereference that occurs within the kernel's handling of procfs access requests. When a local user attempts to access the path /emul/linux/proc/0/stat on a procfs filesystem mounted with the linux compatibility option, the kernel fails to properly validate the pointer references within its internal data structures. This results in the kernel attempting to dereference a NULL pointer, which immediately triggers a kernel panic and system crash. The vulnerability is classified as a software error that violates fundamental memory safety principles and represents a classic example of improper null pointer handling in kernel space. This type of flaw falls under CWE-476 which specifically addresses NULL pointer dereference vulnerabilities in software systems.
The operational impact of this vulnerability is severe and directly affects system availability and stability. A local attacker can reliably cause a denial of service condition that results in complete system crashes, requiring manual reboot to restore normal operations. This vulnerability is particularly concerning because it requires no special privileges beyond local access to the system, making it exploitable by any user with basic system login capabilities. The impact extends beyond simple service disruption as kernel panics can potentially lead to data loss or corruption, especially if the system is in the middle of critical operations. The vulnerability affects multiple NetBSD versions simultaneously, indicating a widespread issue within the kernel implementation that required immediate patching across the affected release lines.
The exploitation of this vulnerability demonstrates a clear path to system compromise through denial of service attacks, which can be classified under the ATT&CK technique T1499.004 for network denial of service. Organizations running affected NetBSD systems should immediately implement the available patches to address this vulnerability, as the window for exploitation is minimal and the impact is severe. System administrators should verify that their procfs filesystems are not mounted with the linux compatibility option if such functionality is not required, as this removes the attack surface for this specific vulnerability. The patching process should include updating to the specific NetBSD versions released after the mentioned dates, which contain the necessary fixes for the NULL pointer dereference issue in the procfs implementation. Additionally, monitoring systems should be configured to detect unusual access patterns to the affected procfs paths, as this may indicate attempted exploitation of the vulnerability.