CVE-2024-43896 in Linux
Summary
by MITRE • 08/26/2024
In the Linux kernel, the following vulnerability has been resolved:
ASoC: cs-amp-lib: Fix NULL pointer crash if efi.get_variable is NULL
Call efi_rt_services_supported() to check that efi.get_variable exists before calling it.
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Analysis
by VulDB Data Team • 09/06/2024
The vulnerability identified as CVE-2024-43896 represents a critical null pointer dereference issue within the Linux kernel's sound subsystem, specifically affecting the cs-amp-lib component used in audio amplifier management. This flaw exists in the Advanced Sound Architecture (ASoC) framework which handles audio codec and amplifier configurations in embedded systems. The vulnerability occurs when the kernel attempts to access the efi.get_variable function pointer without proper validation, leading to a potential system crash or denial of service condition. The issue is particularly concerning as it affects systems that rely on UEFI runtime services for audio hardware configuration, creating a scenario where legitimate audio initialization processes can cause kernel panics.
The technical root cause stems from improper function pointer validation within the audio amplifier library implementation. When the kernel initializes audio hardware components, it attempts to query UEFI variables to configure amplifier settings, but fails to verify that the UEFI runtime services interface is properly available. The efi.get_variable function pointer may be NULL in certain system configurations or during specific boot phases, yet the code proceeds to invoke it directly without checking the validity of this interface. This pattern violates fundamental defensive programming practices and creates an exploitable condition where a simple hardware initialization sequence can result in system instability. The vulnerability aligns with CWE-476 which describes null pointer dereference conditions in software implementations, particularly in kernel space where such faults can have catastrophic consequences for system stability and security.
The operational impact of this vulnerability extends beyond simple system crashes, as it affects the reliability of audio subsystem initialization across various embedded platforms and servers that utilize UEFI firmware interfaces. Systems running Linux kernels that incorporate the affected cs-amp-lib component may experience unexpected termination during audio device enumeration, potentially disrupting audio functionality entirely or causing cascading failures in related subsystems. In enterprise environments, this could manifest as intermittent audio issues in servers or embedded systems, while in consumer devices, it might cause complete audio subsystem failures during boot processes or when audio devices are connected. The vulnerability is particularly dangerous in environments where audio hardware is critical for system diagnostics or user interaction, as it could prevent proper system operation during crucial boot phases. This issue can be classified under ATT&CK technique T1490 which covers data destruction and system instability through kernel-level modifications or exploitation.
Mitigation strategies for CVE-2024-43896 focus on implementing proper function pointer validation before execution, with the primary fix requiring modification of the cs-amp-lib code to call efi_rt_services_supported() prior to invoking efi.get_variable. This approach ensures that the UEFI runtime services interface is properly initialized and available before attempting to access its functions. System administrators should prioritize kernel updates that include this fix, particularly in environments where audio functionality is critical or where systems may encounter edge cases during boot processes. Additional defensive measures include monitoring system logs for kernel panic messages related to audio subsystem initialization and implementing proper error handling in custom audio driver implementations. The fix demonstrates the importance of proper interface validation in kernel code and aligns with security best practices for preventing null pointer dereference conditions in operating system components. Organizations should also consider implementing automated patch management processes to ensure timely deployment of kernel security updates, as this vulnerability could potentially be exploited in targeted attacks against systems that rely heavily on audio hardware initialization sequences.