CVE-2024-57896 is a high-severity use-after-free vulnerability in the Linux kernel's Btrfs filesystem implementation. The flaw occurs during the unmount process in the close_ctree() function, where the cleaner kernel thread responsible for managing delayed allocation workers is stopped and its associated task_struct is freed before all queued workers have completed. Specifically, after the cleaner kthread is stopped via kthread_stop(), some delalloc_workers may still be executing submit_compressed_extents(), which calls btrfs_add_delayed_iput(). This function attempts to wake the cleaner kthread, which has already been destroyed, leading to a use-after-free condition on the task_struct. The vulnerability was identified by Syzbot through kernel address sanitizer (KASAN) reports showing slab-use-after-free errors in kernel locking code. Exploitation could lead to kernel memory corruption, causing system instability, crashes, or potentially privilege escalation due to corrupted kernel data structures. The CVSS 3.1 score of 7.8 reflects high impact on confidentiality, integrity, and availability, with low attack complexity but requiring local privileges (local access with low privileges). The vulnerability affects Linux kernel versions prior to the patch and is related to CWE-416 (Use After Free). No known exploits are reported in the wild yet, but the flaw's nature makes it a significant risk for systems using Btrfs, especially those performing frequent unmount operations. The detailed kernel stack traces confirm the use-after-free triggered during workqueue processing and task_struct lifecycle management.

For European organizations, this vulnerability poses a substantial risk particularly to servers and systems running Linux with Btrfs filesystems. Btrfs is increasingly used in enterprise environments for its advanced features like snapshots and checksums. Exploitation could allow attackers with local access to cause denial of service through kernel crashes or potentially escalate privileges to gain unauthorized control over affected systems. This could lead to data breaches, disruption of critical services, and compromise of sensitive information. Organizations relying on Linux-based infrastructure for cloud services, data centers, or embedded devices could face operational interruptions and increased incident response costs. The vulnerability's requirement for local access limits remote exploitation but insider threats or compromised user accounts could leverage this flaw. Given the high confidentiality, integrity, and availability impact, European entities in finance, healthcare, government, and critical infrastructure sectors should prioritize remediation to prevent exploitation and maintain compliance with data protection regulations such as GDPR.

1. Immediate patching: Apply the latest Linux kernel updates that address CVE-2024-57896 as soon as they become available from trusted Linux distributions or kernel maintainers. 2. Kernel version management: Maintain an inventory of Linux kernel versions in use and prioritize upgrades on systems utilizing Btrfs filesystems. 3. Limit local access: Restrict local user privileges and access to systems running vulnerable kernels to trusted personnel only. Implement strict access controls and monitoring to detect suspicious activities. 4. Use alternative filesystems: Where feasible, consider using more mature and less vulnerable filesystems if Btrfs features are not essential. 5. Monitoring and detection: Deploy kernel integrity monitoring and anomaly detection tools to identify crashes or unusual kernel behavior indicative of exploitation attempts. 6. Harden workqueue and kernel thread management: For organizations developing custom kernels or patches, ensure proper synchronization and lifecycle management of kernel threads and workqueues to avoid similar use-after-free conditions. 7. Incident response preparedness: Develop and test incident response plans to quickly address potential exploitation scenarios involving kernel vulnerabilities.