CVE-2021-47035 is a vulnerability identified in the Linux kernel's IOMMU (Input-Output Memory Management Unit) implementation, specifically related to Intel VT-d (Virtualization Technology for Directed I/O) second-level paging entries. The issue arises from inconsistent permission handling in the page table entries used for IOVA (IO Virtual Address) translation. In the first-level page table, only Read-Only and Read-Write permissions are supported, with the Write-Only (WO) permission being invalid because the PRESENT bit, which implies read permission, must always be set. However, in the second-level page tables, the Linux kernel erroneously allowed Write-Only permissions, creating an inconsistency and potential security risk. This discrepancy could lead to unpredictable behavior or security flaws when the second-level paging entries are used for IOVA translation, potentially allowing unauthorized write access without proper read permissions. The patch removes the Write-Only permission configuration from second-level paging entries to enforce consistent permission handling across both levels, thereby mitigating the risk of exploitation. Although no known exploits are currently reported in the wild, the vulnerability affects the Linux kernel versions identified by the given commit hashes and pertains to systems utilizing Intel VT-d for device virtualization and memory isolation.

For European organizations, the impact of CVE-2021-47035 primarily concerns environments that rely on Linux-based virtualization infrastructures, especially those using Intel VT-d for secure device assignment and memory isolation. This includes cloud service providers, data centers, and enterprises running virtualized workloads on Linux hosts. Exploitation could potentially allow malicious actors or compromised virtual machines to bypass memory access restrictions, leading to unauthorized write operations on memory regions. This could compromise the confidentiality and integrity of data, disrupt virtual machine isolation, and potentially lead to privilege escalation or denial of service. Given the widespread use of Linux in critical infrastructure, telecommunications, and enterprise IT across Europe, failure to address this vulnerability could expose sensitive systems to targeted attacks. However, the absence of known exploits and the technical complexity of exploiting this issue somewhat limit immediate risk, but the potential for future exploitation remains, especially in high-value environments.

European organizations should promptly apply the Linux kernel patches that remove the Write-Only permission from second-level paging entries in the IOMMU VT-d implementation. This involves updating to the latest stable Linux kernel versions that include the fix referenced by the commit hashes. Additionally, organizations should audit their virtualization environments to identify systems using Intel VT-d and ensure they are running patched kernels. Employing strict access controls and monitoring for unusual IOMMU or virtualization-related activities can help detect attempts to exploit this vulnerability. For environments where immediate patching is challenging, consider isolating critical virtual machines and limiting device passthrough capabilities to reduce attack surface. Regularly reviewing kernel security advisories and maintaining an up-to-date vulnerability management process will also help mitigate risks associated with this and similar vulnerabilities.