---
id: CVE-2025-40307
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  exfat: validate cluster allocation bits of the allocation bitmap

  syzbot created an exfat image with cluster bits not set for the allocation
  bitmap
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  exfat: validate cluster allocation bits of the allocation bitmap

  syzbot created an exfat image with cluster bits not set for the allocation
  bitmap. 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: 0.03215
ingestedAt: '2026-08-03T10:24:19.739Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

exfat: validate cluster allocation bits of the allocation bitmap

syzbot created an exfat image with cluster bits not set for the allocation
bitmap. exfat-fs reads and uses the allocation bitmap without checking
this. The problem is that if the start cluster of the allocation bitmap
is 6, cluster 6 can be allocated when creating a directory with mkdir.
exfat zeros out this cluster in exfat_mkdir, which can delete existing
entries. This can reallocate the allocated entries. In addition,
the allocation bitmap is also zeroed out, so cluster 6 can be reallocated.
This patch adds exfat_test_bitmap_range to validate that clusters used for
the allocation bitmap are correctly marked as in-use.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.