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GHSA-6247-F99H-HR72

Vulnerability from github – Published: 2026-10-18 18:31 – Updated: 2026-10-18 18:31

Details

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.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-98684"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-18T16:17:21Z",
    "severity": null
  },
  "details": "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": "GHSA-6247-f99h-hr72",
  "modified": "2026-10-18T18:31:59Z",
  "published": "2026-10-18T18:31:59Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98684"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/aa994489bd835547c191827acc460192e147032d"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/bf84e44ff0ed802778eafd7ecb623635379cb506"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f82242fe3109a3ef72f429540b5bdde08fbfb0e4"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

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

Vulnerability from cvelistv5 – Published: 2026-10-18 15:45 – Updated: 2026-10-19 09:23

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 6847 records in the last 180 days details

References

3 references

URL	Tags
https://git.kernel.org/stable/c/f82242fe3109a3ef7…
https://git.kernel.org/stable/c/bf84e44ff0ed80277…
https://git.kernel.org/stable/c/aa994489bd835547c…

Impacted products

2 products

Vendor	Product	Version
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)
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)

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JSON

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/smb2ops.c"
          ],
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          "vendor": "Linux",
          "versions": [
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              "status": "affected",
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              "versionType": "git"
            },
            {
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              "version": "2f9f4a2d0e6fcf0673ed51195e06e47abe966900",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "5e397c943424de94879830e72c95f2679e297a76",
              "versionType": "git"
            },
            {
              "lessThan": "5.11",
              "status": "affected",
              "version": "5.10.50",
              "versionType": "semver"
            },
            {
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              "status": "affected",
              "version": "5.12.17",
              "versionType": "semver"
            },
            {
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              "status": "affected",
              "version": "5.13.2",
              "versionType": "semver"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/smb2ops.c"
          ],
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          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.14"
            },
            {
              "lessThan": "5.14",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.56",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.10",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "vulnerable": true
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                },
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          "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/bf84e44ff0ed802778eafd7ecb623635379cb506"
        },
        {
          "url": "https://git.kernel.org/stable/c/aa994489bd835547c191827acc460192e147032d"
        }
      ],
      "title": "smb: client: flush and commit data before querying allocated ranges",
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98684",
    "datePublished": "2026-10-18T15:45:52.828Z",
    "dateReserved": "2026-09-25T10:25:14.364Z",
    "dateUpdated": "2026-10-19T09:23:54.479Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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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.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
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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