CVE-2022-48631 is a vulnerability identified in the Linux kernel's ext4 filesystem implementation. Specifically, the flaw exists in the ext4 extent parsing logic within the ext4_ext_binsearch_idx() function. This function assumes that the extent header has been validated previously, but it lacks a critical check to ensure that the number of entries (eh_entries) is non-zero when the depth (eh_depth) is greater than zero. Extents are data structures used by ext4 to efficiently map file blocks. When eh_entries is zero while eh_depth is greater than zero, the EXT_FIRST_INDEX() and EXT_LAST_INDEX() macros return invalid values, leading to the kernel attempting to access invalid memory or perform illegal operations. This results in a kernel BUG and an invalid opcode exception, causing the kernel to crash (kernel panic). The vulnerability can be triggered during file read operations that involve extent mapping, as demonstrated by the kernel call trace provided. The patch for this vulnerability adds an additional validation step in the __ext4_ext_check() function to verify that eh_entries is not zero when eh_depth is greater than zero, preventing the invalid memory access and subsequent kernel crash. This vulnerability affects Linux kernel versions prior to the patch and can be exploited by providing specially crafted ext4 filesystem metadata or files that trigger the faulty extent parsing logic. There are no known exploits in the wild at this time, and the vulnerability does not have an assigned CVSS score. However, the impact is a denial of service through kernel panic, which can disrupt system availability.

For European organizations, this vulnerability poses a risk primarily to systems running Linux with ext4 filesystems, which is a common default filesystem on many Linux distributions widely used in enterprise, government, and cloud environments across Europe. Exploitation leads to a kernel crash, causing denial of service (DoS). This can disrupt critical services, especially in environments where uptime is essential such as financial institutions, healthcare providers, and public sector infrastructure. While the vulnerability does not appear to allow privilege escalation or data corruption directly, repeated or targeted exploitation could be used to cause persistent outages or to facilitate further attacks by forcing reboots or triggering recovery procedures. Organizations relying on Linux-based servers, virtual machines, or embedded devices using ext4 are at risk. The lack of known exploits reduces immediate threat but does not eliminate the risk, especially as attackers may develop exploits once the vulnerability details become widely known. The impact on confidentiality and integrity is low, but availability impact is medium to high depending on the criticality of affected systems.

1. Apply the official Linux kernel patch that adds the necessary validation check in the ext4 extent parsing code as soon as it becomes available from your Linux distribution vendor. 2. Regularly update Linux kernel versions to incorporate security patches and improvements. 3. For critical systems, consider implementing kernel live patching solutions to minimize downtime during patch application. 4. Monitor system logs for kernel BUG messages or crashes related to ext4 operations to detect potential exploitation attempts. 5. Use filesystem integrity checking tools to verify ext4 metadata consistency and detect malformed extents that could trigger the vulnerability. 6. Limit access to systems and filesystems that could be used to trigger the vulnerability, especially restricting untrusted users from mounting or manipulating ext4 filesystems. 7. Employ intrusion detection systems (IDS) and endpoint detection and response (EDR) solutions capable of detecting unusual kernel crashes or filesystem anomalies. 8. In virtualized environments, isolate and monitor guest VMs to prevent propagation of kernel crashes or denial of service conditions.