CVE-2026-43158 is a high-severity vulnerability in the Linux kernel's XFS filesystem related to incorrect freemap adjustments when adding extended attributes (xattrs) to leaf blocks. The flaw causes an assertion failure due to overlapping free space and entries arrays, leading to filesystem shutdown. The issue arises from improper updates to the freemap entries, which track free space within leaf blocks, allowing collisions between used and free space. This vulnerability has been fixed by adjusting freemap entries to prevent overlap with the entries array.