CVE-2026-98684 (GCVE-0-2026-98684)

Vulnerability from cvelistv5 – Published: 2026-10-18 15:45 – Updated: 2026-10-19 09:23
VLAI
Title
smb: client: flush and commit data before querying allocated ranges
Summary
In the Linux kernel, the following vulnerability has been resolved: smb: client: flush and commit data before querying allocated ranges The mode 0 / FALLOC_FL_KEEP_SIZE fallocate emulation for small interior ranges in smb3_simple_fallocate_range() issues FSCTL_QUERY_ALLOCATED_RANGES and zero-fills any sub-range the server reports as an unallocated hole, to force block allocation without changing file contents. This is unsafe against Windows servers. Per the Win32 documentation, FSCTL_QUERY_ALLOCATED_RANGES only reports ranges that *may* contain nonzero data and is explicitly not coherent with recently written data: "a call to FSCTL_QUERY_ALLOCATED_RANGES [after writing to a network file] would not necessarily return a correct list of allocated regions. To ensure coherency [...] flush the data to the file" fsx (generic/363) reproduces the resulting corruption against Windows Server 2022: a range is written, an uncached read returns the data, yet the next FSCTL_QUERY_ALLOCATED_RANGES on that range reports it as a whole hole, so the emulation overwrites live data with zeroes. A network trace confirmed the WRITE, the READ returning data and the query returning an empty range list within microseconds. Samba does not exhibit this; its query is coherent with the written data. Write back the dirty pages, drain any outstanding I/O and issue an SMB2 FLUSH to force the server to commit the data before querying the allocated ranges, so the query reflects the data actually present. With this, generic/363 passes against both Windows Server 2022 and Samba over 100000 fsx operations.
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6820 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 966a3cb7c7db786452a87afdc3b48858fc4d4d6b , < f82242fe3109a3ef72f429540b5bdde08fbfb0e4 (git)
Affected: 966a3cb7c7db786452a87afdc3b48858fc4d4d6b , < bf84e44ff0ed802778eafd7ecb623635379cb506 (git)
Affected: 966a3cb7c7db786452a87afdc3b48858fc4d4d6b , < aa994489bd835547c191827acc460192e147032d (git)
Affected: c406bb9ece6ef63721daab106f132ff4b4234e81 (git)
Affected: 2f9f4a2d0e6fcf0673ed51195e06e47abe966900 (git)
Affected: 5e397c943424de94879830e72c95f2679e297a76 (git)
Affected: 5.10.50 , < 5.11 (semver)
Affected: 5.12.17 , < 5.13 (semver)
Affected: 5.13.2 , < 5.14 (semver)
guessed Create a notification for this product.
Linux Linux Affected: 5.14
Unaffected: 0 , < 5.14 (semver)
Unaffected: 6.18.56 , ≤ 6.18.* (semver)
Unaffected: 7.2.10 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
Show details on NVD website
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          "programFiles": [
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      "cpeApplicability": [
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: flush and commit data before querying allocated ranges\n\nThe mode 0 / FALLOC_FL_KEEP_SIZE fallocate emulation for small interior\nranges in smb3_simple_fallocate_range() issues\nFSCTL_QUERY_ALLOCATED_RANGES and zero-fills any sub-range the server\nreports as an unallocated hole, to force block allocation without\nchanging file contents.\n\nThis is unsafe against Windows servers.  Per the Win32 documentation,\nFSCTL_QUERY_ALLOCATED_RANGES only reports ranges that *may* contain\nnonzero data and is explicitly not coherent with recently written data:\n\n  \"a call to FSCTL_QUERY_ALLOCATED_RANGES [after writing to a network\n   file] would not necessarily return a correct list of allocated\n   regions.  To ensure coherency [...] flush the data to the file\"\n\nfsx (generic/363) reproduces the resulting corruption against Windows\nServer 2022: a range is written, an uncached read returns the data, yet\nthe next FSCTL_QUERY_ALLOCATED_RANGES on that range reports it as a whole\nhole, so the emulation overwrites live data with zeroes.  A network trace\nconfirmed the WRITE, the READ returning data and the query returning an\nempty range list within microseconds.  Samba does not exhibit this; its\nquery is coherent with the written data.\n\nWrite back the dirty pages, drain any outstanding I/O and issue an SMB2\nFLUSH to force the server to commit the data before querying the\nallocated ranges, so the query reflects the data actually present.\n\nWith this, generic/363 passes against both Windows Server 2022 and Samba\nover 100000 fsx operations."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:23:54.479Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
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          "url": "https://git.kernel.org/stable/c/f82242fe3109a3ef72f429540b5bdde08fbfb0e4"
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        {
          "url": "https://git.kernel.org/stable/c/bf84e44ff0ed802778eafd7ecb623635379cb506"
        },
        {
          "url": "https://git.kernel.org/stable/c/aa994489bd835547c191827acc460192e147032d"
        }
      ],
      "title": "smb: client: flush and commit data before querying allocated ranges",
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    "datePublished": "2026-10-18T15:45:52.828Z",
    "dateReserved": "2026-09-25T10:25:14.364Z",
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    "state": "PUBLISHED"
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      "percentile": "0.05811"
    },
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      "cve": "CVE-2026-98684",
      "id": "msrc_CVE-2026-98684",
      "initial_release_date": "2026-10-20T22:24:08.000Z",
      "product_status:known_affected": "2",
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      "status": "final",
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        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: flush and commit data before querying allocated ranges\n\nThe mode 0 / FALLOC_FL_KEEP_SIZE fallocate emulation for small interior\nranges in smb3_simple_fallocate_range() issues\nFSCTL_QUERY_ALLOCATED_RANGES and zero-fills any sub-range the server\nreports as an unallocated hole, to force block allocation without\nchanging file contents.\n\nThis is unsafe against Windows servers.  Per the Win32 documentation,\nFSCTL_QUERY_ALLOCATED_RANGES only reports ranges that *may* contain\nnonzero data and is explicitly not coherent with recently written data:\n\n  \"a call to FSCTL_QUERY_ALLOCATED_RANGES [after writing to a network\n   file] would not necessarily return a correct list of allocated\n   regions.  To ensure coherency [...] flush the data to the file\"\n\nfsx (generic/363) reproduces the resulting corruption against Windows\nServer 2022: a range is written, an uncached read returns the data, yet\nthe next FSCTL_QUERY_ALLOCATED_RANGES on that range reports it as a whole\nhole, so the emulation overwrites live data with zeroes.  A network trace\nconfirmed the WRITE, the READ returning data and the query returning an\nempty range list within microseconds.  Samba does not exhibit this; its\nquery is coherent with the written data.\n\nWrite back the dirty pages, drain any outstanding I/O and issue an SMB2\nFLUSH to force the server to commit the data before querying the\nallocated ranges, so the query reflects the data actually present.\n\nWith this, generic/363 passes against both Windows Server 2022 and Samba\nover 100000 fsx operations."
          }
        ],
        "id": "CVE-2026-98684",
        "lastModified": "2026-10-19T10:19:32.823",
        "metrics": {},
        "published": "2026-10-18T16:17:21.770",
        "references": [
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        "vulnStatus": "Received"
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    "redhat_vex": {
      "aggregate_severity": "Low",
      "current_release_date": "2026-10-22T03:00:08+00:00",
      "cve": "CVE-2026-98684",
      "id": "CVE-2026-98684",
      "initial_release_date": "2026-10-18T00:00:00+00:00",
      "product_status:known_affected": "236",
      "product_status:known_not_affected": "42",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: smb: client: flush and commit data before querying allocated ranges",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-98684.json",
      "version": "3"
    }
  }
}



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