CVE-2024-56548 is a vulnerability identified in the Linux kernel's HFS+ filesystem driver. The issue arises from improper handling of device logical block sizes, particularly when using loop devices with ioctl LOOP_SET_BLOCK_SIZE to change block sizes dynamically. The HFS+ driver allocates blocks based on an initial logical block size but may subsequently perform I/O operations with a different size, leading to out-of-bounds memory writes. This discrepancy occurs because the driver queries the device logical block size multiple times without consistent synchronization, causing a use-after-free condition as detected by Kernel Address Sanitizer (KASAN). The vulnerability manifests when the hfsplus_read_wrapper function calls hfsplus_submit_bio with mismatched I/O sizes, potentially corrupting kernel memory. The flaw was demonstrated by mounting an HFS+ filesystem on loop devices with varying block sizes (512, 1024, 4096 bytes), triggering a KASAN slab-use-after-free error. This vulnerability is rooted in the filesystem code's failure to maintain a stable minimum I/O size, which was addressed by initializing a min_io_size variable to the maximum of HFSPLUS_SECTOR_SIZE and the first observed logical block size. The patch ensures consistent block size usage during I/O operations, preventing out-of-bounds writes and memory corruption. While no known exploits are currently reported in the wild, the vulnerability could be leveraged by local attackers or malicious code with the ability to mount or manipulate HFS+ filesystems on affected Linux kernels. The issue affects specific Linux kernel versions identified by commit hashes, indicating it is present in recent kernel releases prior to the fix. No CVSS score has been assigned yet, but the technical details and KASAN reports confirm a serious memory safety flaw in a widely used kernel component.

For European organizations, the impact of CVE-2024-56548 depends on their use of Linux systems that mount HFS+ filesystems, particularly in environments using loop devices or virtualized setups where block sizes might be manipulated. The vulnerability could lead to kernel memory corruption, causing system instability, crashes, or potential privilege escalation if exploited. This poses risks to data confidentiality and integrity, as kernel memory corruption can be a vector for arbitrary code execution or denial of service. Organizations relying on Linux servers, desktops, or embedded devices that support HFS+ (common in interoperability scenarios with Apple devices) may be exposed. The threat is more pronounced in development, testing, or virtualization environments where loop devices are frequently used. Although exploitation requires local access and the ability to mount or manipulate filesystems, the widespread deployment of Linux in European enterprises, government, and critical infrastructure sectors means that unpatched systems could be vulnerable to targeted attacks or accidental crashes. The lack of known exploits reduces immediate risk, but the severity of kernel memory corruption warrants prompt attention to prevent future exploitation.

European organizations should prioritize updating their Linux kernels to versions that include the fix for CVE-2024-56548. Specifically, they should apply patches that initialize and consistently use the min_io_size variable in the HFS+ driver to prevent out-of-bounds writes. System administrators should audit systems that mount HFS+ filesystems, especially those using loop devices or virtual block devices with configurable block sizes. Where possible, avoid mounting HFS+ filesystems on vulnerable kernel versions or restrict mounting privileges to trusted users only. Implement kernel hardening techniques such as Kernel Address Sanitizer (KASAN) in testing environments to detect similar memory issues proactively. Additionally, monitoring kernel logs for KASAN or related memory corruption warnings can help identify attempts to trigger this vulnerability. For environments requiring HFS+ support, consider isolating such workloads in containers or virtual machines with updated kernels to minimize impact. Finally, maintain strict access controls and limit local user privileges to reduce the risk of exploitation by unprivileged users.