CVE-2021-47373 is a vulnerability identified in the Linux kernel, specifically within the irqchip/gic-v3-its component responsible for managing interrupt routing in ARM architectures. The issue arises in the function its_vpe_irq_domain_alloc during error handling in its_vpe_init(). When an error occurs, there is an off-by-one error in the count of Virtual Processing Elements (VPEs) to be freed, leading to a potential resource leak. This means that one more VPE than allocated could be attempted to be freed, which can cause undefined behavior such as memory corruption or kernel instability. The fix involves correcting the loop index to accurately reflect the number of allocated VPEs, preventing the leak. Although this vulnerability does not have known exploits in the wild, it affects Linux kernel versions identified by the commit hash 7d75bbb4bc1ad90386776459d37e4ddfe605671e and related versions. The vulnerability is subtle and relates to low-level kernel interrupt management, which is critical for system stability and security, especially on ARM-based systems using the GICv3 interrupt controller with ITS (Interrupt Translation Service).

For European organizations, the impact of CVE-2021-47373 primarily concerns systems running Linux on ARM architectures that utilize the GICv3 ITS interrupt controller, such as embedded devices, IoT infrastructure, telecom equipment, and certain cloud or edge computing platforms. A resource leak in kernel interrupt management can lead to degraded system performance, potential denial of service due to kernel instability or crashes, and in worst cases, could be leveraged as part of a chain of exploits to escalate privileges or bypass security controls. While no direct exploits are known, the vulnerability could be exploited by attackers with local access or through compromised software components to destabilize critical systems. This is particularly relevant for sectors relying on ARM-based Linux devices, including telecommunications, industrial control systems, and critical infrastructure in Europe. The vulnerability may also affect developers and vendors who build custom Linux kernels for ARM platforms, necessitating patching to maintain system reliability and security.

European organizations should prioritize updating their Linux kernel versions to include the patch that fixes the off-by-one error in its_vpe_irq_domain_alloc. Specifically, they should track kernel updates from trusted sources and apply them promptly to all ARM-based Linux systems using GICv3 ITS. For embedded and IoT devices, coordination with hardware vendors and firmware providers is essential to ensure updated kernel images are deployed. Additionally, organizations should implement rigorous kernel integrity monitoring and system stability checks to detect anomalies potentially caused by this vulnerability. Limiting local access to critical systems and enforcing strict access controls can reduce the risk of exploitation. For development teams, reviewing custom kernel code and interrupt handling implementations for similar off-by-one or resource management errors is advisable. Finally, maintaining comprehensive incident response plans that include kernel-level vulnerabilities will help mitigate potential impacts if exploitation attempts arise.