CVE-2021-47502 is a vulnerability identified in the Linux kernel's ALSA System on Chip (ASoC) codec driver for the wcd934x audio codec. The issue arises from improper handling of the channel mapping list within the Digital Audio Interface (DAI) channel list management. Specifically, the vulnerability occurs because the code does not correctly verify whether a channel is already assigned to a DAI channel list before adding it again. This can lead to the same channel being added multiple times to different DAI channel lists, resulting in corruption of the channel lists. The root cause is the absence of checks to ensure that a channel is free before adding it and that a channel exists on the list before attempting to remove it. This flaw was not detected earlier due to limited testing scenarios involving simple amixer command sequences. The patch for this vulnerability introduces proper validation to prevent duplicate channel additions and ensures safe removal operations, thereby maintaining the integrity of the channel lists. Although the vulnerability affects the Linux kernel, it is specifically related to the audio subsystem's codec driver, which is a component used in various embedded and general-purpose Linux systems.

For European organizations, the impact of CVE-2021-47502 is primarily on systems running Linux kernels with the affected wcd934x codec driver, which is commonly found in mobile devices, embedded systems, and some laptops. The corruption of channel lists could lead to audio subsystem instability, potential denial of service (system crashes or kernel panics), or unpredictable behavior in audio processing. While this vulnerability does not directly expose data confidentiality or integrity risks, the resulting system instability could disrupt critical services relying on audio subsystems, such as communication tools, multimedia applications, or embedded control systems. In sectors like telecommunications, automotive, and industrial control where Linux-based embedded devices are prevalent, this could translate into operational disruptions. However, since exploitation does not appear to be trivial and no known exploits are reported in the wild, the immediate risk is moderate. Nonetheless, organizations deploying Linux-based devices with this codec should prioritize patching to avoid potential service interruptions.

To mitigate CVE-2021-47502, European organizations should: 1) Identify all Linux systems using the affected wcd934x codec driver, particularly embedded devices and laptops running custom or vendor-specific Linux kernels. 2) Apply the official Linux kernel patches that address the channel mapping list handling, ensuring the kernel version includes the fix. 3) For devices where kernel updates are not immediately feasible, consider disabling or restricting the use of the affected audio codec driver if audio functionality is non-critical. 4) Implement rigorous testing of audio subsystem functionality post-patching to confirm stability and absence of regressions. 5) Monitor vendor advisories and Linux kernel mailing lists for any updates or related vulnerabilities. 6) Incorporate this vulnerability into vulnerability management and patching schedules, prioritizing devices in critical infrastructure or communication roles. 7) Educate system administrators and embedded device maintainers about the importance of maintaining updated kernel versions to prevent such low-level subsystem issues.