What’s Vulnerable › Vulnerabilities

CVE-2025-40307: exfat: validate cluster allocation bits of the allocation bitmap

• Severity: high (CVSS 7.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-12-08 · updated 2026-10-15

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 kernel: 5.7 — fixed in 6.18

How to fix

Upgrade to a fixed version: Linux kernel 6.18. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/13c1d24803d5b0446b3f6f0fdd67e07ac1fdc7bf
• https://git.kernel.org/stable/c/67ce8034dc0278ddd88cad93d4218a945180dddd
• https://git.kernel.org/stable/c/6bc58b4c53795ab5fe00648344aa7d9d61175f90
• https://git.kernel.org/stable/c/79c1587b6cda74deb0c86fc7ba194b92958c793c
• https://git.kernel.org/stable/c/87f827d53bd0688597bda63ae95908e2ad39bac0

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