FKIE_CVE-2026-72170
Vulnerability from fkie_nvd - Published: 2026-08-15 06:21 - Updated: 2026-08-23 13:16
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved:
9p: skip nlink update in cacheless mode to fix WARN_ON
v9fs_dec_count() unconditionally calls drop_nlink() on regular files,
even when the inode's nlink is already zero. In cacheless mode the
client refetches inode metadata from the server (the source of truth)
on every operation, so by the time v9fs_remove() returns, the locally
cached nlink may already reflect the post-unlink value:
1. Client initiates unlink, server processes it and sets nlink to 0
2. Client refetches inode metadata (nlink=0) before unlink returns
3. Client's v9fs_remove() completes successfully
4. Client calls v9fs_dec_count() which calls drop_nlink() on nlink=0
This race is easily triggered under heavy unlink workloads, such as
stress-ng's unlink stressor, producing the following warning:
WARNING: fs/inode.c:417 at drop_nlink+0x4c/0xc8
Call trace:
drop_nlink+0x4c/0xc8
v9fs_remove+0x1e0/0x250 [9p]
v9fs_vfs_unlink+0x20/0x38 [9p]
vfs_unlink+0x13c/0x258
...
In cacheless mode the server is authoritative and the inode is on its
way out, so locally adjusting nlink buys nothing. Skip v9fs_dec_count()
entirely when neither CACHE_META nor CACHE_LOOSE is set, which both
avoids the warning and removes a class of nlink races (two concurrent
unlinkers observing nlink > 0 and both calling drop_nlink()) that an
nlink == 0 guard alone would only narrow rather than close.
References
Impacted products
| Vendor | Product | Version |
|---|
{
"affected": [
{
"affectedData": [
{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"fs/9p/vfs_inode.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"lessThan": "6086469f7d469549bfd070348b717a6e43736200",
"status": "affected",
"version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb",
"versionType": "git"
},
{
"lessThan": "ab257019cb72f467b55c95384d99c94e3908b928",
"status": "affected",
"version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb",
"versionType": "git"
},
{
"lessThan": "4ec4ebe40c82cb4c60756732f6593055d010c59c",
"status": "affected",
"version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb",
"versionType": "git"
},
{
"lessThan": "a5a682b016ef5b5384e28f6d652d47a8f8e73d37",
"status": "affected",
"version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb",
"versionType": "git"
},
{
"lessThan": "de79c3f3643841b8659a71958df7cf2a66bfd409",
"status": "affected",
"version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb",
"versionType": "git"
},
{
"lessThan": "8d610017c992de705b304d3d727a6e3a86af6149",
"status": "affected",
"version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb",
"versionType": "git"
},
{
"lessThan": "8faccac11e1369adddf5d80f4a45af93f13b2e1a",
"status": "affected",
"version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb",
"versionType": "git"
},
{
"lessThan": "574aa0b4799470ac814479f1138d19efe6262255",
"status": "affected",
"version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb",
"versionType": "git"
}
]
},
{
"defaultStatus": "affected",
"product": "Linux",
"programFiles": [
"fs/9p/vfs_inode.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "4.17"
},
{
"lessThan": "4.17",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.10.*",
"status": "unaffected",
"version": "5.10.266",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.15.*",
"status": "unaffected",
"version": "5.15.217",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.1.*",
"status": "unaffected",
"version": "6.1.184",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"version": "6.6.145",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"version": "6.12.97",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.18.*",
"status": "unaffected",
"version": "6.18.40",
"versionType": "semver"
},
{
"lessThanOrEqual": "7.1.*",
"status": "unaffected",
"version": "7.1.5",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.2",
"versionType": "original_commit_for_fix"
}
]
}
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
],
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\n9p: skip nlink update in cacheless mode to fix WARN_ON\n\nv9fs_dec_count() unconditionally calls drop_nlink() on regular files,\neven when the inode\u0027s nlink is already zero. In cacheless mode the\nclient refetches inode metadata from the server (the source of truth)\non every operation, so by the time v9fs_remove() returns, the locally\ncached nlink may already reflect the post-unlink value:\n\n 1. Client initiates unlink, server processes it and sets nlink to 0\n 2. Client refetches inode metadata (nlink=0) before unlink returns\n 3. Client\u0027s v9fs_remove() completes successfully\n 4. Client calls v9fs_dec_count() which calls drop_nlink() on nlink=0\n\nThis race is easily triggered under heavy unlink workloads, such as\nstress-ng\u0027s unlink stressor, producing the following warning:\n\n WARNING: fs/inode.c:417 at drop_nlink+0x4c/0xc8\n Call trace:\n drop_nlink+0x4c/0xc8\n v9fs_remove+0x1e0/0x250 [9p]\n v9fs_vfs_unlink+0x20/0x38 [9p]\n vfs_unlink+0x13c/0x258\n ...\n\nIn cacheless mode the server is authoritative and the inode is on its\nway out, so locally adjusting nlink buys nothing. Skip v9fs_dec_count()\nentirely when neither CACHE_META nor CACHE_LOOSE is set, which both\navoids the warning and removes a class of nlink races (two concurrent\nunlinkers observing nlink \u003e 0 and both calling drop_nlink()) that an\nnlink == 0 guard alone would only narrow rather than close."
}
],
"id": "CVE-2026-72170",
"lastModified": "2026-08-23T13:16:41.387",
"metrics": {
"cvssMetricV31": [
{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "LOCAL",
"availabilityImpact": "HIGH",
"baseScore": 7.8,
"baseSeverity": "HIGH",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "LOW",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"exploitabilityScore": 1.8,
"impactScore": 5.9,
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"type": "Secondary"
}
]
},
"published": "2026-08-15T06:21:35.100",
"references": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/4ec4ebe40c82cb4c60756732f6593055d010c59c"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/574aa0b4799470ac814479f1138d19efe6262255"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/6086469f7d469549bfd070348b717a6e43736200"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/8d610017c992de705b304d3d727a6e3a86af6149"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/8faccac11e1369adddf5d80f4a45af93f13b2e1a"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/a5a682b016ef5b5384e28f6d652d47a8f8e73d37"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/ab257019cb72f467b55c95384d99c94e3908b928"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/de79c3f3643841b8659a71958df7cf2a66bfd409"
}
],
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"vulnStatus": "Received"
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
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.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- 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.
- 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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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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