{"id":"CVE-2025-40307","title":"In the Linux kernel, the following vulnerability has been resolved:\n\nexfat: validate cluster allocation bits of the allocation bitmap\n\nsyzbot created an exfat image with cluster bits not set for the allocation\nbitmap","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nexfat: validate cluster allocation bits of the allocation bitmap\n\nsyzbot created an exfat image with cluster bits not set for the allocation\nbitmap. exfat-fs reads and …","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","published":"2025-12-08","updated":"2026-08-03","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2025-40307","references":[{"url":"https://git.kernel.org/stable/c/13c1d24803d5b0446b3f6f0fdd67e07ac1fdc7bf","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/67ce8034dc0278ddd88cad93d4218a945180dddd","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/6bc58b4c53795ab5fe00648344aa7d9d61175f90","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/79c1587b6cda74deb0c86fc7ba194b92958c793c","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"tags":["nvd"],"epss":0.00147,"epssPercentile":0.04289,"ingestedAt":"2026-08-03T10:24:19.739Z","slug":"CVE-2025-40307","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nexfat: validate cluster allocation bits of the allocation bitmap\n\nsyzbot created an exfat image with cluster bits not set for the allocation\nbitmap. exfat-fs reads and uses the allocation bitmap without checking\nthis. The problem is that if the start cluster of the allocation bitmap\nis 6, cluster 6 can be allocated when creating a directory with mkdir.\nexfat zeros out this cluster in exfat_mkdir, which can delete existing\nentries. This can reallocate the allocated entries. In addition,\nthe allocation bitmap is also zeroed out, so cluster 6 can be reallocated.\nThis patch adds exfat_test_bitmap_range to validate that clusters used for\nthe allocation bitmap are correctly marked as in-use.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}