CVE-2021-47116 is a vulnerability identified in the Linux kernel's ext4 filesystem implementation. Specifically, the issue arises in the ext4_mb_init_backend function, which is responsible for managing block group metadata initialization. The vulnerability manifests as a memory leak that occurs on an error path when the filesystem is corrupted with an illegally large s_log_groups_per_flex parameter. This parameter controls the number of block groups per flex group in ext4, and an invalidly large value can trigger the leak. The flaw was discovered by syzbot, an automated kernel fuzzing tool, indicating that it is a robustness issue triggered by malformed filesystem metadata. The memory leak could potentially lead to resource exhaustion if exploited repeatedly or in a targeted manner. However, the vulnerability requires the presence of a corrupted ext4 filesystem with the specific illegal parameter value, which is not a common state under normal operation. There are no known exploits in the wild at this time, and no CVSS score has been assigned. The Linux kernel maintainers have addressed the issue by fixing the error path to properly release allocated memory, preventing the leak. This vulnerability is primarily a stability and resource management issue rather than a direct code execution or privilege escalation flaw.

For European organizations, the impact of CVE-2021-47116 is primarily related to system stability and availability. Systems running Linux with ext4 filesystems could experience memory leaks if exposed to corrupted filesystem metadata containing an illegal s_log_groups_per_flex value. While this condition is not typical, it could be induced by attackers with local access or through crafted disk images or storage media. The memory leak could degrade system performance or lead to denial of service through resource exhaustion, especially on critical servers or embedded devices relying on ext4. However, the lack of known exploits and the requirement for a corrupted filesystem limit the immediate risk. Organizations with extensive Linux deployments, particularly those using ext4 on servers, desktops, or embedded systems, should be aware of this vulnerability. The impact is less severe than vulnerabilities allowing remote code execution or privilege escalation but still warrants attention to maintain system reliability and prevent potential denial of service scenarios.

To mitigate CVE-2021-47116, European organizations should apply the official Linux kernel patches that fix the memory leak in ext4_mb_init_backend as soon as they become available from their Linux distribution vendors. Regularly updating the kernel and filesystem utilities ensures that such robustness issues are addressed. Additionally, organizations should implement filesystem integrity monitoring and validation to detect and prevent corrupted ext4 filesystems, which could trigger this vulnerability. Employing storage media validation and avoiding the use of untrusted or suspicious disk images can reduce the risk of encountering malformed filesystem metadata. For critical systems, consider implementing resource usage monitoring to detect abnormal memory consumption that could indicate exploitation attempts. Finally, restricting local access to trusted users and limiting the ability to mount or manipulate filesystems can reduce the attack surface.