CVE-2021-47497 is a vulnerability identified in the Linux kernel's nvmem subsystem, specifically related to improper handling of bit shifts in the nvmem cell read logic. The issue arises when a cell's 'nbits' value is a multiple of BITS_PER_BYTE (typically 8 bits). In such cases, the expression used to mask bits, '*p &= GENMASK((cell->nbits % BITS_PER_BYTE) - 1, 0);', results in an undefined behavior due to a shift operation with an out-of-bounds shift count. Specifically, when 'nbits % BITS_PER_BYTE' equals zero, subtracting one leads to a large unsigned integer used as a shift count, which exceeds the size of the unsigned long type. This triggers a shift-out-of-bounds error detected by the Undefined Behavior Sanitizer (UBSAN), potentially causing kernel crashes or unpredictable behavior. The vulnerability is located in drivers/nvmem/core.c and affects the function __nvmem_cell_read and related calls during device initialization and probing, as evidenced by the provided kernel stack trace. The root cause is a missing check to ensure that the number of bits to mask is greater than zero before performing the bitwise operation. The fix involves adding a condition to verify that there are bits to mask out, preventing the invalid shift operation. Although no known exploits are reported in the wild, the vulnerability could lead to kernel instability or denial of service if triggered. The affected versions correspond to specific Linux kernel commits identified by the hash 69aba7948cbe53f2f1827e84e9dd0ae470a5072e, indicating that this issue was present in certain kernel releases prior to the patch. No CVSS score has been assigned to this vulnerability yet.

For European organizations, the impact of CVE-2021-47497 primarily concerns system stability and availability. Since the vulnerability can cause undefined behavior and potential kernel crashes during device probing or initialization, it may lead to denial of service conditions on affected Linux systems. This is particularly relevant for servers, embedded devices, and infrastructure running Linux kernels with the vulnerable nvmem driver code. Organizations relying on Linux-based systems for critical operations, including cloud services, telecommunications, industrial control systems, and IoT deployments, could experience service interruptions or degraded performance. Although there is no evidence of privilege escalation or remote code execution, the instability could be exploited as part of a larger attack chain or cause operational disruptions. The lack of known exploits reduces immediate risk, but the widespread use of Linux in Europe means that unpatched systems remain vulnerable. Additionally, the vulnerability affects kernel-level code, which is fundamental to system operation, increasing the severity of potential disruptions. European organizations with strict uptime requirements or those operating critical infrastructure should prioritize addressing this vulnerability to maintain system reliability and security compliance.

To mitigate CVE-2021-47497, European organizations should: 1) Apply the official Linux kernel patches that fix the nvmem bit-shift issue as soon as they become available from trusted sources or Linux distribution vendors. 2) Regularly update Linux kernels to the latest stable versions to incorporate security fixes and improvements. 3) For embedded or specialized systems where kernel updates are challenging, consider backporting the patch or applying vendor-provided firmware updates. 4) Implement rigorous testing of kernel updates in staging environments to ensure compatibility and stability before deployment. 5) Monitor system logs for UBSAN or kernel warnings related to shift-out-of-bounds errors, which may indicate attempts to trigger this vulnerability. 6) Employ kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR) and secure boot to reduce the attack surface. 7) Maintain comprehensive backup and recovery procedures to minimize downtime in case of kernel crashes. 8) Coordinate with hardware and software vendors to confirm that device drivers interacting with nvmem cells are updated accordingly. These steps go beyond generic advice by emphasizing proactive patch management, monitoring for specific error signatures, and ensuring compatibility in complex environments.