{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2025-40307","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2025-04-16T07:20:57.185Z","datePublished":"2025-12-08T00:46:32.659Z","dateUpdated":"2026-08-19T16:27:52.404Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-19T16:27:52.404Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nexfat: validate cluster allocation bits of the allocation bitmap\n\nsyzbot created an exfat image with cluster bits not set for the allocation\nbitmap. exfat-fs reads and uses the allocation bitmap without checking\nthis. The problem is that if the start cluster of the allocation bitmap\nis 6, cluster 6 can be allocated when creating a directory with mkdir.\nexfat zeros out this cluster in exfat_mkdir, which can delete existing\nentries. This can reallocate the allocated entries. In addition,\nthe allocation bitmap is also zeroed out, so cluster 6 can be reallocated.\nThis patch adds exfat_test_bitmap_range to validate that clusters used for\nthe allocation bitmap are correctly marked as in-use."}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The vulnerable code is reached by getting a crafted exFAT image mounted from a local block device, loop file, or removable medium and then issuing a local `mkdir()`; there is no network consumer of `exfat_allocate_bitmap()`.\nAC:L - The attacker fully controls the image: clearing the bitmap's own allocation bit and pointing `start_clu` at a low cluster makes `exfat_find_free_bitmap()` deterministically return that cluster on the very first allocation, so a single `mkdir` reliably zeroes the live bitmap with no race, heap shaping, or memory-layout dependency.\nPR:L - Direct `mount()` needs CAP_SYS_ADMIN, but ubiquitous privileged mount brokers (udisks2, systemd-mount, autofs, Android vold) let an unprivileged local user get an attacker-supplied exFAT volume or loop image mounted rw, after which any user with write access to the mount can run the triggering `mkdir`.\nUI:N - The attacker requests the mount through the automount broker and runs `mkdir` themselves; on a kiosk or shared workstation inserting their own exFAT stick achieves the same, with no action required from any other user or administrator.\nS:U - The corruption and its consequences are confined to the kernel and filesystem that own the mount; no VM, IOMMU, container, or other security-authority boundary is crossed.\nC:H - Once the bitmap is zeroed the allocator re-hands out clusters that are still live, so a newly created file is backed by clusters holding the root directory, other files' data, and the allocation bitmap itself — reading that file discloses their full contents, an unbounded read of co-resident data on the shared volume rather than a small bounded leak.\nI:H - This is the core defect: the kernel zeroes and overwrites in-use on-disk metadata (\"can delete existing entries\") and reallocates already-allocated clusters, so attacker-controlled file writes land directly in directory entries and in the live in-kernel allocation bitmap, giving unbounded modification of structures the filesystem subsequently trusts.\nA:H - The zeroed bitmap makes every `exfat_clear_bitmap()` fail with `-EIO`, desyncs `used_clusters` into `exfat_fs_error_ratelimit()`, and produces aliased/looping cluster chains that yield task hangs and the syzbot-reported deadlock WARNING; with `errors=panic`, `panic_on_warn`, or `panic_on_oops` this is a full panic, and the volume is left permanently unusable."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/exfat/balloc.c"],"versions":[{"version":"1acf1a564b6034b5af1e7fb23cb98cb3bb4f6003","lessThan":"87f827d53bd0688597bda63ae95908e2ad39bac0","status":"affected","versionType":"git"},{"version":"1acf1a564b6034b5af1e7fb23cb98cb3bb4f6003","lessThan":"67ce8034dc0278ddd88cad93d4218a945180dddd","status":"affected","versionType":"git"},{"version":"1acf1a564b6034b5af1e7fb23cb98cb3bb4f6003","lessThan":"6bc58b4c53795ab5fe00648344aa7d9d61175f90","status":"affected","versionType":"git"},{"version":"1acf1a564b6034b5af1e7fb23cb98cb3bb4f6003","lessThan":"13c1d24803d5b0446b3f6f0fdd67e07ac1fdc7bf","status":"affected","versionType":"git"},{"version":"1acf1a564b6034b5af1e7fb23cb98cb3bb4f6003","lessThan":"79c1587b6cda74deb0c86fc7ba194b92958c793c","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/exfat/balloc.c"],"versions":[{"version":"5.7","status":"affected"},{"version":"0","lessThan":"5.7","status":"unaffected","versionType":"semver"},{"version":"6.1.183","lessThanOrEqual":"6.1.*","status":"unaffected","versionType":"semver"},{"version":"6.6.148","lessThanOrEqual":"6.6.*","status":"unaffected","versionType":"semver"},{"version":"6.12.58","lessThanOrEqual":"6.12.*","status":"unaffected","versionType":"semver"},{"version":"6.17.8","lessThanOrEqual":"6.17.*","status":"unaffected","versionType":"semver"},{"version":"6.18","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.7","versionEndExcluding":"6.1.183"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.7","versionEndExcluding":"6.6.148"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.7","versionEndExcluding":"6.12.58"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.7","versionEndExcluding":"6.17.8"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.7","versionEndExcluding":"6.18"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/87f827d53bd0688597bda63ae95908e2ad39bac0"},{"url":"https://git.kernel.org/stable/c/67ce8034dc0278ddd88cad93d4218a945180dddd"},{"url":"https://git.kernel.org/stable/c/6bc58b4c53795ab5fe00648344aa7d9d61175f90"},{"url":"https://git.kernel.org/stable/c/13c1d24803d5b0446b3f6f0fdd67e07ac1fdc7bf"},{"url":"https://git.kernel.org/stable/c/79c1587b6cda74deb0c86fc7ba194b92958c793c"}],"title":"exfat: validate cluster allocation bits of the allocation bitmap","x_generator":{"engine":"bippy-1.2.0"}}}}