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CVE-2025-40307 (GCVE-0-2025-40307)

Vulnerability from cvelistv5 – Published: 2025-12-08 00:46 – Updated: 2026-08-19 16:27
VLAI
Title
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.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 1acf1a564b6034b5af1e7fb23cb98cb3bb4f6003 , < 87f827d53bd0688597bda63ae95908e2ad39bac0 (git)
Affected: 1acf1a564b6034b5af1e7fb23cb98cb3bb4f6003 , < 67ce8034dc0278ddd88cad93d4218a945180dddd (git)
Affected: 1acf1a564b6034b5af1e7fb23cb98cb3bb4f6003 , < 6bc58b4c53795ab5fe00648344aa7d9d61175f90 (git)
Affected: 1acf1a564b6034b5af1e7fb23cb98cb3bb4f6003 , < 13c1d24803d5b0446b3f6f0fdd67e07ac1fdc7bf (git)
Affected: 1acf1a564b6034b5af1e7fb23cb98cb3bb4f6003 , < 79c1587b6cda74deb0c86fc7ba194b92958c793c (git)
guessed Create a notification for this product.
Linux Linux Affected: 5.7
Unaffected: 0 , < 5.7 (semver)
Unaffected: 6.1.183 , ≤ 6.1.* (semver)
Unaffected: 6.6.148 , ≤ 6.6.* (semver)
Unaffected: 6.12.58 , ≤ 6.12.* (semver)
Unaffected: 6.17.8 , ≤ 6.17.* (semver)
Unaffected: 6.18 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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              "status": "unaffected",
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              "negate": false,
              "operator": "OR"
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      "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": [
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            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
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              "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\u0027s 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\u0027 data, and the allocation bitmap itself \u2014 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."
            }
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    "datePublished": "2025-12-08T00:46:32.659Z",
    "dateReserved": "2025-04-16T07:20:57.185Z",
    "dateUpdated": "2026-08-19T16:27:52.404Z",
    "state": "PUBLISHED"
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            "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."
          }
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        "lastModified": "2026-08-19T17:18:35.510",
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                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
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      "cve": "CVE-2025-40307",
      "id": "CVE-2025-40307",
      "initial_release_date": "2025-12-08T00:00:00+00:00",
      "product_status:known_affected": "184",
      "product_status:known_not_affected": "90",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: exfat: validate cluster allocation bits of the allocation bitmap",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-40307.json",
      "version": "3"
    },
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      "current_release_date": "2026-09-11T01:53:59Z",
      "cve": "CVE-2025-40307",
      "id": "CVE-2025-40307",
      "initial_release_date": "2025-12-09T00:24:28Z",
      "product_status:first_fixed": "2",
      "product_status:known_affected": "870",
      "product_status:recommended": "289",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2025-40307",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2025-40307.json",
      "version": "46"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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