CVE-2021-47325 is a vulnerability identified in the Linux kernel, specifically within the ARM System Memory Management Unit (SMMU) driver code. The issue arises in the function arm_smmu_iova_to_phys_hard(), which is responsible for address translation in the ARM SMMU. During certain exception handling paths, the function fails to properly decrement the reference count of the 'smmu' device object after it was incremented by arm_smmu_rpm_get(). This leads to a reference count leak, meaning that the system incorrectly tracks the usage of the device object, potentially preventing its proper release. The root cause is that in error scenarios, the code does not jump to the appropriate cleanup label ('out'), causing the decrement operation to be skipped. This flaw can cause resource leakage in the kernel, which over time may lead to increased memory consumption or exhaustion of kernel objects related to the SMMU device. While this vulnerability does not directly enable code execution or privilege escalation, the resource leak can degrade system stability and availability, especially on systems heavily reliant on ARM SMMU for memory management. The vulnerability affects specific Linux kernel versions identified by commit hashes, and a fix involves correcting the control flow to ensure the reference count is decremented in all error paths. No known exploits are reported in the wild, and no CVSS score has been assigned yet.

For European organizations, the impact of CVE-2021-47325 primarily concerns systems running Linux on ARM architectures that utilize the ARM SMMU, such as embedded devices, network equipment, or servers using ARM-based processors. The reference count leak can cause gradual resource depletion, potentially leading to system instability, degraded performance, or crashes. This can affect availability of critical services, especially in environments where uptime is essential, such as telecommunications infrastructure, industrial control systems, or cloud services hosted on ARM-based hardware. Although the vulnerability does not directly compromise confidentiality or integrity, the resulting denial of service conditions could disrupt business operations or critical infrastructure. Organizations with ARM-based Linux deployments in Europe should be aware of this issue, as it may impact the reliability of their systems if left unpatched.

To mitigate this vulnerability, European organizations should prioritize updating their Linux kernel to versions that include the patch fixing CVE-2021-47325. Since the issue is in the kernel code, applying vendor-provided kernel updates or patches is the most effective approach. For environments where immediate patching is not feasible, monitoring system resource usage related to the ARM SMMU device and kernel object reference counts can help detect abnormal leaks early. Implementing automated alerts for unusual memory or resource consumption may provide early warning signs. Additionally, organizations should review their ARM-based Linux deployments to assess exposure and consider isolating or limiting access to vulnerable systems until patches are applied. Engaging with hardware and software vendors to confirm patch availability and deployment timelines is also recommended. Finally, maintaining robust backup and recovery procedures will help mitigate potential availability impacts caused by system instability.