exfat: validate cluster allocation bits of 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 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.

Timeline

1. Dec 8, 2025, 12:46 AM UTCCVE published
2. Oct 15, 2026, 9:59 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: total

3. Oct 15, 2026, 10:02 PM UTCRecord last updated

Affected versions

• Linux Linux

  From 1acf1a564b6034b5af1e7fb23cb98cb3bb4f6003 · fixed in 87f827d53bd0688597bda63ae95908e2ad39bac0; From 1acf1a564b6034b5af1e7fb23cb98cb3bb4f6003 · fixed in 67ce8034dc0278ddd88cad93d4218a945180dddd; From 1acf1a564b6034b5af1e7fb23cb98cb3bb4f6003 · fixed in 6bc58b4c53795ab5fe00648344aa7d9d61175f90; From 1acf1a564b6034b5af1e7fb23cb98cb3bb4f6003 · fixed in 13c1d24803d5b0446b3f6f0fdd67e07ac1fdc7bf; From 1acf1a564b6034b5af1e7fb23cb98cb3bb4f6003 · fixed in 79c1587b6cda74deb0c86fc7ba194b92958c793c

• Linux Linux

  5.7

• KernelLinux

  From 5.7.0 · fixed in 6.1.183; From 6.2.0 · fixed in 6.6.148; From 6.7.0 · fixed in 6.12.58; From 6.13.0 · fixed in 6.17.8

References 5