CVE-2026-98684
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:
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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.
Technical details traces, logs and code from the original report
"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"
CVSS
NVD hasn't assigned a CVSS score to this CVE (common since the April 2026 policy change).
Exploitation probability (EPSS)
- Probability of exploitation in the next 30 days
- 0.17 %
- Percentile among all scored CVEs
- 5
- Score date
- 10/20/2026
EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).
Affected technologies (1)
⚠ AI-inferred from the description — NVD hasn't analyzed this CVE yet, these aren't verified CPEs.
References
Raw JSON (NVD)
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{
"id": "CVE-2026-98684",
"cveTags": [],
"metrics": {},
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "966a3cb7c7db786452a87afdc3b48858fc4d4d6b",
"lessThan": "f82242fe3109a3ef72f429540b5bdde08fbfb0e4",
"versionType": "git"
},
{
"status": "affected",
"version": "966a3cb7c7db786452a87afdc3b48858fc4d4d6b",
"lessThan": "bf84e44ff0ed802778eafd7ecb623635379cb506",
"versionType": "git"
},
{
"status": "affected",
"version": "966a3cb7c7db786452a87afdc3b48858fc4d4d6b",
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"versionType": "git"
},
{
"status": "affected",
"version": "c406bb9ece6ef63721daab106f132ff4b4234e81",
"versionType": "git"
},
{
"status": "affected",
"version": "2f9f4a2d0e6fcf0673ed51195e06e47abe966900",
"versionType": "git"
},
{
"status": "affected",
"version": "5e397c943424de94879830e72c95f2679e297a76",
"versionType": "git"
},
{
"status": "affected",
"version": "5.10.50",
"lessThan": "5.11",
"versionType": "semver"
},
{
"status": "affected",
"version": "5.12.17",
"lessThan": "5.13",
"versionType": "semver"
},
{
"status": "affected",
"version": "5.13.2",
"lessThan": "5.14",
"versionType": "semver"
}
],
"programFiles": [
"fs/smb/client/smb2ops.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "5.14"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "5.14",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "6.18.56",
"versionType": "semver",
"lessThanOrEqual": "6.18.*"
},
{
"status": "unaffected",
"version": "7.2.10",
"versionType": "semver",
"lessThanOrEqual": "7.2.*"
},
{
"status": "unaffected",
"version": "7.3",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"fs/smb/client/smb2ops.c"
],
"defaultStatus": "affected"
}
]
}
],
"published": "2026-10-18T16:17:21.770",
"references": [
{
"url": "https://git.kernel.org/stable/c/aa994489bd835547c191827acc460192e147032d",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/bf84e44ff0ed802778eafd7ecb623635379cb506",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/f82242fe3109a3ef72f429540b5bdde08fbfb0e4",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
],
"vulnStatus": "Received",
"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."
}
],
"lastModified": "2026-10-19T10:19:32.823",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}