CVE-2025-40244

A flaw was discovered in the Linux kernel’s HFS+ filesystem driver where the __hfsplus_ext_cache_extent() function could operate on an uninitialized value. This was identified by the Kernel Memory Sanitizer during testing and can lead to undefined behavior — including kernel instability or panic — when filesystem write operations traverse this code path.

A moderate severity flaw was found in the Linux kernel's HFS+ (hfsplus) filesystem driver. The hfs_find_init() function allocated its search data with kmalloc() without zero-initializing it, so when a B-tree lookup performed by __hfsplus_ext_cache_extent() found no matching extent record during a write operation on an HFS+ filesystem, the function compared and operated on uninitialized memory. A local user with write access to an HFS+ volume could trigger this path, leading to undefined kernel behavior such as kernel instability or a panic, which is a denial of service. Red Hat Product Security rated this flaw Moderate (CVSS 3.1 score 4.7, AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H) because exploitation requires local privileges plus write access to an HFS+ filesystem, has high attack complexity, and affects availability only; this differs from the upstream CVE.org rating of Important (7.8). Per the current assessment, Red Hat Enterprise Linux 6 is out of support scope, and the maintained Red Hat Enterprise Linux 7 through 10 streams (including kernel-rt) and Red Hat In-Vehicle OS 1.1 are not affected because the vulnerable code is not present in those products.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options don't meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.