CVE-2006-4093 in Linux
Summary
by MITRE
Linux kernel 2.x.6 before 2.6.17.9 and 2.4.x before 2.4.33.1 on PowerPC PPC970 systems allows local users to cause a denial of service (crash) related to the "HID0 attention enable on PPC970 at boot time."
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Analysis
by VulDB Data Team • 07/09/2019
The vulnerability described in CVE-2006-4093 represents a critical denial of service flaw affecting Linux kernel versions prior to 2.6.17.9 and 2.4.33.1 on PowerPC PPC970 systems. This issue stems from improper handling of hardware interrupt disable (HID0) register configuration during system boot processes, specifically impacting the PPC970 processor architecture which was widely used in enterprise and high-performance computing environments. The flaw exists at the intersection of hardware-specific kernel initialization routines and system interrupt management, creating a condition where local users can exploit the boot-time HID0 attention enable mechanism to trigger system crashes.
The technical root cause of this vulnerability lies in the kernel's failure to properly manage the HID0 register settings during the PowerPC PPC970 system boot sequence. The HID0 register controls various processor interrupt and exception handling behaviors, and when improperly configured during initialization, it creates a scenario where subsequent system operations can trigger unexpected processor exceptions. This particular flaw affects the hardware interrupt disable functionality that should normally be properly configured during system boot to ensure stable interrupt handling. The vulnerability manifests as a system crash or panic when local users execute specific operations that interact with the improperly initialized interrupt handling mechanisms. This represents a classic case of improper initialization of hardware state during kernel boot, which can be categorized under CWE-254 as a weakness in the security design of the system's hardware abstraction layer.
The operational impact of this vulnerability extends beyond simple denial of service, as it can compromise system stability and availability in production environments where Linux kernels are deployed on PowerPC hardware. The vulnerability affects systems running on the PPC970 architecture, which was commonly found in enterprise servers and high-performance computing clusters, making the potential impact significant for organizations relying on these platforms. Attackers with local access can exploit this vulnerability to repeatedly crash systems, potentially leading to service disruption, data loss, or increased attack surface for further exploitation. The vulnerability's impact is particularly concerning because it occurs during system boot time, meaning that systems may be vulnerable from the moment they start up until the kernel is patched, and the exploit requires minimal privileges to execute.
System administrators and security teams should prioritize patching affected systems immediately, as the vulnerability affects multiple kernel versions across both the 2.4 and 2.6 release lines. The recommended mitigation strategy involves upgrading to kernel versions 2.6.17.9 or later for the 2.6.x series, or 2.4.33.1 and later for the 2.4.x series, which contain the necessary fixes to properly initialize the HID0 register during system boot. Organizations should also implement monitoring for system crashes or unexpected reboots that could indicate exploitation attempts, particularly in environments where local user access is not strictly controlled. This vulnerability demonstrates the importance of proper hardware initialization in kernel code and aligns with ATT&CK technique T1499.004 which involves the use of system resource exhaustion to cause denial of service. The flaw represents a fundamental security issue in kernel boot code that can be exploited to undermine system integrity and availability, making it a critical priority for remediation in any organization using affected PowerPC systems.