CVE-2022-49879 is a vulnerability in the Linux kernel's ext4 filesystem implementation. The issue arises from improper validation of the rec_len field in directory entries. The rec_len field specifies the length of a directory entry and must be a multiple of 4. If a corrupted or maliciously crafted filesystem image contains directory entries with invalid rec_len values, it can trigger a kernel BUG in the ext4_rec_len_to_disk() function, which is called during directory indexing operations in make_indexed_dir(). This BUG manifests as a kernel panic or crash, leading to denial of service. The root cause is that the ext4 filesystem code did not sufficiently validate directory entries before processing them, allowing malformed entries to cause a kernel-level fault. The fix introduced involves adding a call to ext4_check_dir_entry() to validate directory entries and return an error (-EFSCORRUPTED) if invalid entries are detected, preventing the BUG from being triggered. This vulnerability affects Linux kernel versions prior to the patch and can be exploited by mounting or accessing a corrupted ext4 filesystem image. There are no known exploits in the wild as of the published date, and no CVSS score has been assigned yet.

For European organizations, this vulnerability poses a risk primarily to systems running Linux with ext4 filesystems, which is the default filesystem for many Linux distributions widely used in enterprise, cloud, and server environments. Exploitation can cause kernel crashes leading to denial of service, potentially disrupting critical services, applications, or infrastructure relying on Linux servers. This can affect availability of systems hosting web services, databases, or internal applications. While the vulnerability does not appear to allow privilege escalation or remote code execution directly, the induced system instability can be leveraged in targeted attacks to cause operational disruptions. Organizations using containerized environments or virtual machines with ext4-backed storage may also be impacted if they mount or interact with corrupted ext4 images. The lack of known exploits suggests limited immediate risk, but the vulnerability should be addressed proactively to avoid potential future exploitation, especially in sectors where uptime and data integrity are critical, such as finance, healthcare, and government.

European organizations should apply the Linux kernel patches that include the fix for CVE-2022-49879 as soon as they become available from their Linux distribution vendors. Until patches are applied, administrators should avoid mounting or accessing untrusted or suspicious ext4 filesystem images that could be malformed. Implementing strict validation and scanning of filesystem images before deployment can reduce risk. Monitoring kernel logs for BUG() messages related to ext4 can help detect attempted exploitation or filesystem corruption. In environments using container or VM images, ensure images are verified and scanned for integrity before use. Additionally, maintaining robust backup and recovery procedures will mitigate impact in case of crashes. Organizations should also consider deploying kernel crash dump analysis tools to investigate any unexpected kernel panics to identify if this vulnerability is being triggered. Finally, restricting access to systems that handle filesystem images to trusted personnel and processes reduces the attack surface.