CVE-2025-40307: Linux

High severity, CVSS 7.8. EPSS: 0.1% chance of exploitation in the next 30 days.

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: from 5.7, before 6.1.183 (fixed in 6.1.183); from 6.2, before 6.6.148 (fixed in 6.6.148); from 6.7, before 6.12.58 (fixed in 6.12.58); from 6.13, before 6.17.8 (fixed in 6.17.8)

Published 2025-12-08. Last modified 2026-08-19.