# CVE-2025-40307

## Summary

- **CVE ID:** CVE-2025-40307
- **Severity:** HIGH
- **CVSS Score:** 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Dec 8, 2025
- **Last Modified:** Aug 19, 2026

## Description

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.

## Affected Products

- Linux — Linux (1acf1a564b6034b5af1e7fb23cb98cb3bb4f6003)
- Linux — Linux (5.7)
- Linux — Linux (0)
- Linux — Linux (6.12.58)
- Linux — Linux (6.17.8)
- Linux — Linux (6.18)
- Linux — Linux (6.6.148)
- Linux — Linux (6.1.183)

## References

- [CNA](https://git.kernel.org/stable/c/6bc58b4c53795ab5fe00648344aa7d9d61175f90)
- [CNA](https://git.kernel.org/stable/c/13c1d24803d5b0446b3f6f0fdd67e07ac1fdc7bf)
- [CNA](https://git.kernel.org/stable/c/79c1587b6cda74deb0c86fc7ba194b92958c793c)
- [CNA](https://git.kernel.org/stable/c/67ce8034dc0278ddd88cad93d4218a945180dddd)
- [CNA](https://git.kernel.org/stable/c/87f827d53bd0688597bda63ae95908e2ad39bac0)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.15%
- **EPSS Percentile:** 4.3

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._