CVE-2025-21804 is a vulnerability identified in the Linux kernel specifically related to the PCI driver for Renesas R-Car platform (rcar-ep). The issue arises in the function rcar_pcie_parse_outbound_ranges(), which uses the devm_request_mem_region() macro to request memory resources. The vulnerability is due to the use of a stack-based string variable to store a dynamically computed resource name, which is then passed as an argument to devm_request_mem_region(). Because this string is not properly null-terminated or managed, it can lead to undefined behavior including the possibility of reading beyond the intended memory boundaries. This can manifest as corrupted or garbage output when inspecting /proc/iomem, and in rare cases, can cause the system to crash due to accessing unmapped memory beyond the stack. The root cause is the incorrect variable usage for the resource name, which was fixed by replacing the outbound_name variable with the name of the previously requested resource to ensure proper string handling and memory safety. This vulnerability affects Linux kernel versions containing the specified commit hashes prior to the fix. Although no known exploits are currently reported in the wild, the flaw could potentially cause system instability or denial of service on affected systems using the rcar-ep PCI driver, which is relevant for embedded and automotive Linux deployments on Renesas R-Car platforms.

For European organizations, the impact of CVE-2025-21804 depends largely on the use of Linux systems running on Renesas R-Car platforms, which are commonly found in automotive, industrial, and embedded systems. Organizations involved in automotive manufacturing, industrial automation, or critical infrastructure that rely on these platforms could face system instability or unexpected crashes, potentially leading to operational disruptions. While this vulnerability does not directly expose confidentiality or integrity risks, the availability impact through system crashes or undefined behavior could affect production lines, vehicle systems, or embedded control units. Given the increasing adoption of Linux-based embedded systems in European automotive and industrial sectors, the vulnerability could have a moderate operational impact if exploited or triggered unintentionally. However, since exploitation requires triggering the specific PCI driver code path and no remote exploit is known, the threat is more relevant to local or targeted attacks or accidental system faults.

To mitigate CVE-2025-21804, European organizations should: 1) Apply the official Linux kernel patches that fix the rcar-ep PCI driver to ensure proper memory region request handling. 2) For embedded and automotive Linux deployments using Renesas R-Car platforms, coordinate with hardware and software vendors to update kernel versions or apply vendor-provided patches promptly. 3) Implement rigorous testing and validation of kernel updates in embedded environments to detect any instability or crashes related to PCI resource management. 4) Monitor system logs and /proc/iomem outputs for anomalies or garbage data that could indicate attempts to trigger the vulnerability. 5) Restrict access to systems running vulnerable kernels to trusted personnel only, as exploitation requires local code execution or privileged access. 6) Incorporate this vulnerability into risk assessments for embedded Linux systems and update incident response plans to handle potential denial-of-service scenarios caused by kernel crashes.