CVE-2026-89713
In the Linux kernel, the following vulnerability has been resolved:
NFSD: check truncate permission under inode lock
nfsd_setattr() checks whether a size update needs NFSD_MAY_TRUNC before it takes inode_lock(). The comparison uses the file size sampled by that unlocked read, but the actual ATTR_SIZE update is applied later under inode_lock() by notify_change().
This leaves a TOCTOU window for append-only files. If a client sends a SETATTR that does not shrink the file at the time of the unlocked sample, a concurrent append can extend the file before nfsd_setattr() takes inode_lock(). notify_change() then applies a real truncation without the NFSD_MAY_TRUNC check that rejects IS_APPEND(inode). The VFS truncate syscall paths perform their own append-only checks before calling notify_change(), so NFSD must make this decision against the locked size it is about to change.
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Split the write-count acquisition from the truncation permission check. Keep get_write_access() before the locked setattr work, then recheck whether the requested size is below i_size_read(inode) after inode_lock() has been acquired and before notify_change(ATTR_SIZE). This also avoids the plain unlocked inode->i_size load.
CVSS
- Versión: 3.1
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
- Puntuación base: 9.1
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.61%
- Percentil entre todas las CVEs puntuadas: 48
- Fecha de la puntuación: 6/10/2026
EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).
🎯 Técnicas ATT&CK
Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.
- Explotación
T1190Exploit Public-Facing Applicationinitial access60 %
Inferido por reglas deterministas a partir del vector CVSS y la CWE. Solo orientativo.
🛡️ Mitigaciones ATT&CK que cubren estas técnicas
Tecnologías afectadas (1)
⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.
Referencias
JSON original (NVD)
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{
"id": "CVE-2026-89713",
"cveTags": [],
"metrics": {
"cvssMetricV31": [
{
"type": "Secondary",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"cvssData": {
"scope": "UNCHANGED",
"version": "3.1",
"baseScore": 9.1,
"attackVector": "NETWORK",
"baseSeverity": "CRITICAL",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H",
"integrityImpact": "HIGH",
"userInteraction": "NONE",
"attackComplexity": "LOW",
"availabilityImpact": "HIGH",
"privilegesRequired": "NONE",
"confidentialityImpact": "NONE"
},
"impactScore": 5.2,
"exploitabilityScore": 3.9
}
]
},
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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{
"status": "affected",
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{
"status": "affected",
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{
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"lessThan": "4.10",
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{
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"lessThan": "4.11",
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],
"programFiles": [
"fs/nfsd/vfs.c"
],
"defaultStatus": "unaffected"
},
{
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{
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"version": "0",
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{
"status": "unaffected",
"version": "6.12.109",
"versionType": "semver",
"lessThanOrEqual": "6.12.*"
},
{
"status": "unaffected",
"version": "6.18.50",
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},
{
"status": "unaffected",
"version": "7.2.4",
"versionType": "semver",
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{
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"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
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],
"programFiles": [
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],
"defaultStatus": "affected"
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],
"published": "2026-09-11T20:19:58.743",
"references": [
{
"url": "https://git.kernel.org/stable/c/3afa17d93ba8c925f49370c816c6dae5112d8c24",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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{
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"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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{
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"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/d8352da196349182e1afd5a93308256cddc0a97d",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
],
"vulnStatus": "Received",
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nNFSD: check truncate permission under inode lock\n\nnfsd_setattr() checks whether a size update needs NFSD_MAY_TRUNC\nbefore it takes inode_lock(). The comparison uses the file size sampled\nby that unlocked read, but the actual ATTR_SIZE update is applied later\nunder inode_lock() by notify_change().\n\nThis leaves a TOCTOU window for append-only files. If a client sends a\nSETATTR that does not shrink the file at the time of the unlocked\nsample, a concurrent append can extend the file before nfsd_setattr()\ntakes inode_lock(). notify_change() then applies a real truncation\nwithout the NFSD_MAY_TRUNC check that rejects IS_APPEND(inode). The VFS\ntruncate syscall paths perform their own append-only checks before\ncalling notify_change(), so NFSD must make this decision against the\nlocked size it is about to change.\n\nSplit the write-count acquisition from the truncation permission check.\nKeep get_write_access() before the locked setattr work, then recheck\nwhether the requested size is below i_size_read(inode) after inode_lock()\nhas been acquired and before notify_change(ATTR_SIZE). This also avoids\nthe plain unlocked inode->i_size load."
}
],
"lastModified": "2026-09-13T07:17:37.013",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}