CVE-2024-47757 is a vulnerability identified in the Linux kernel's nilfs2 filesystem implementation. Specifically, the issue resides in the function nilfs_btree_check_delete(), which is responsible for verifying whether a b-tree entry deletion would cause degeneration to direct mapping. The vulnerability arises because this function can perform an out-of-bounds (OOB) memory read when attempting to retrieve the maximum key from the root node of the b-tree if that root node contains no entries. Under normal circumstances, such a scenario is unlikely because the nilfs2 filesystem and its associated tools (e.g., mkfs.nilfs2) do not create b-tree mappings with zero child nodes. However, if a b-tree root node is read from a device that is improperly configured or corrupted to have zero entries, this OOB read can occur. This memory access outside the intended buffer can lead to undefined behavior, including potential kernel crashes or information disclosure. The fix implemented involves adding a check to detect and handle the case where the root node has no entries, thereby preventing the out-of-bounds access. No known exploits are currently reported in the wild, and the vulnerability was published on October 21, 2024. The affected versions are identified by a specific commit hash, indicating that this is a recent and targeted fix in the Linux kernel source code.

For European organizations, the impact of CVE-2024-47757 depends largely on their use of the nilfs2 filesystem within Linux environments. Nilfs2 is a log-structured filesystem designed for continuous snapshotting and is less commonly used compared to ext4 or XFS, but it is still deployed in certain specialized or legacy systems. If exploited, the out-of-bounds read could lead to kernel instability or crashes, resulting in denial of service (DoS) conditions. In some scenarios, OOB reads can be leveraged to leak sensitive kernel memory, potentially exposing confidential information. However, exploitation requires that the attacker can induce or control the reading of a malformed nilfs2 b-tree root node with zero entries, which is a non-trivial condition. The vulnerability does not appear to allow privilege escalation or remote code execution directly. European organizations operating critical infrastructure, research institutions, or enterprises with Linux servers using nilfs2 could face service disruptions or data exposure risks. Given the lack of known exploits, the immediate risk is moderate, but the potential for future exploitation exists, especially if attackers discover methods to craft malicious nilfs2 filesystem images or devices.

1. Patch Management: Apply the latest Linux kernel updates that include the fix for CVE-2024-47757 as soon as they become available. Monitor kernel release notes and security advisories from trusted sources. 2. Filesystem Usage Review: Assess whether nilfs2 is in use within your environment. If nilfs2 is not required, consider migrating data to more widely supported and actively maintained filesystems like ext4 or XFS to reduce attack surface. 3. Input Validation and Device Control: Restrict access to devices and storage media that could contain malformed nilfs2 filesystems. Implement strict controls on mounting filesystems from untrusted sources. 4. Monitoring and Logging: Enhance system monitoring to detect unusual kernel errors or crashes related to filesystem operations, which could indicate attempted exploitation. 5. Incident Response Preparedness: Develop and test incident response plans for kernel-level vulnerabilities, including rapid patch deployment and system recovery procedures. 6. Kernel Hardening: Employ kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR) and strict memory protections to reduce the impact of potential memory corruption vulnerabilities.