FKIE_CVE-2026-89696
Vulnerability from fkie_nvd - Published: 2026-09-11 20:19 - Updated: 2026-09-14 13:19
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved:
nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref
When CONFIG_NFSD_V4_2_INTER_SSC is enabled, nfsd4_putfh() can return
success with fh_dentry and fh_export both NULL if fh_verify() returns
nfserr_stale and putfh->no_verify is true. The NFSD4_FH_FOREIGN flag
is set, but the compound dispatch loop only uses this flag to bypass
the nfserr_nofilehandle check -- it does not prevent subsequent ops
from running with a NULL fh_dentry.
A remote client can exploit this by crafting a COMPOUND that includes
an inter-SSC COPY (which causes check_if_stalefh_allowed() to set
no_verify=true on the saved PUTFH) with an additional op inserted
between the source PUTFH and SAVEFH. For example, SETATTR calls
fh_want_write() which dereferences fh_export->ex_path.mnt without
calling fh_verify() first, causing a NULL pointer dereference in the
nfsd kthread.
Fix this by gating the dispatch loop: when NFSD4_FH_FOREIGN is set
and fh_dentry is NULL, only OP_SAVEFH (needed for the inter-SSC flow)
and ops with ALLOWED_WITHOUT_FH (which don't need a resolved
filehandle) may proceed. All other ops receive nfserr_stale, per
RFC 7862 Section 15.2.3 which specifies that foreign filehandle
validation is deferred to the consuming operation and NFS4ERR_STALE
returned at that point.
References
Impacted products
| Vendor | Product | Version |
|---|
{
"affected": [
{
"affectedData": [
{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"fs/nfsd/nfs4proc.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"lessThan": "ffdc844e673d2bcb2af8c8c3eef8cdea59d0bf32",
"status": "affected",
"version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e",
"versionType": "git"
},
{
"lessThan": "00c84f4eec715e501efc080a5670114189e42507",
"status": "affected",
"version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e",
"versionType": "git"
},
{
"lessThan": "2d9846fd1c767920fddd4bde30eb35cd2969df13",
"status": "affected",
"version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e",
"versionType": "git"
},
{
"lessThan": "977e6f006a7a3ffc4216ae6034f768f8de6fd138",
"status": "affected",
"version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e",
"versionType": "git"
},
{
"lessThan": "35f248bd40b47b229d4999581df45b97daadd977",
"status": "affected",
"version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e",
"versionType": "git"
},
{
"lessThan": "311f7d926630940650447cbd1c932b076b40a6c4",
"status": "affected",
"version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e",
"versionType": "git"
},
{
"lessThan": "bf4d338dc8625d70c7f2cb0657d66851a7ac9154",
"status": "affected",
"version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e",
"versionType": "git"
},
{
"lessThan": "c59738a00aa51b16adc1b5ceb7c80877168efb4d",
"status": "affected",
"version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e",
"versionType": "git"
}
]
},
{
"defaultStatus": "affected",
"product": "Linux",
"programFiles": [
"fs/nfsd/nfs4proc.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "5.6"
},
{
"lessThan": "5.6",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.10.*",
"status": "unaffected",
"version": "5.10.270",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.15.*",
"status": "unaffected",
"version": "5.15.221",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.1.*",
"status": "unaffected",
"version": "6.1.188",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"version": "6.6.157",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"version": "6.12.109",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.18.*",
"status": "unaffected",
"version": "6.18.50",
"versionType": "semver"
},
{
"lessThanOrEqual": "7.2.*",
"status": "unaffected",
"version": "7.2.4",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.3-rc1",
"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\nnfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref\n\nWhen CONFIG_NFSD_V4_2_INTER_SSC is enabled, nfsd4_putfh() can return\nsuccess with fh_dentry and fh_export both NULL if fh_verify() returns\nnfserr_stale and putfh-\u003eno_verify is true. The NFSD4_FH_FOREIGN flag\nis set, but the compound dispatch loop only uses this flag to bypass\nthe nfserr_nofilehandle check -- it does not prevent subsequent ops\nfrom running with a NULL fh_dentry.\n\nA remote client can exploit this by crafting a COMPOUND that includes\nan inter-SSC COPY (which causes check_if_stalefh_allowed() to set\nno_verify=true on the saved PUTFH) with an additional op inserted\nbetween the source PUTFH and SAVEFH. For example, SETATTR calls\nfh_want_write() which dereferences fh_export-\u003eex_path.mnt without\ncalling fh_verify() first, causing a NULL pointer dereference in the\nnfsd kthread.\n\nFix this by gating the dispatch loop: when NFSD4_FH_FOREIGN is set\nand fh_dentry is NULL, only OP_SAVEFH (needed for the inter-SSC flow)\nand ops with ALLOWED_WITHOUT_FH (which don\u0027t need a resolved\nfilehandle) may proceed. All other ops receive nfserr_stale, per\nRFC 7862 Section 15.2.3 which specifies that foreign filehandle\nvalidation is deferred to the consuming operation and NFS4ERR_STALE\nreturned at that point."
}
],
"id": "CVE-2026-89696",
"lastModified": "2026-09-14T13:19:19.897",
"metrics": {
"cvssMetricV31": [
{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "NETWORK",
"availabilityImpact": "HIGH",
"baseScore": 7.5,
"baseSeverity": "HIGH",
"confidentialityImpact": "NONE",
"integrityImpact": "NONE",
"privilegesRequired": "NONE",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"version": "3.1"
},
"exploitabilityScore": 3.9,
"impactScore": 3.6,
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"type": "Secondary"
}
]
},
"published": "2026-09-11T20:19:56.717",
"references": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/00c84f4eec715e501efc080a5670114189e42507"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/2d9846fd1c767920fddd4bde30eb35cd2969df13"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/311f7d926630940650447cbd1c932b076b40a6c4"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/35f248bd40b47b229d4999581df45b97daadd977"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/977e6f006a7a3ffc4216ae6034f768f8de6fd138"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/bf4d338dc8625d70c7f2cb0657d66851a7ac9154"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/c59738a00aa51b16adc1b5ceb7c80877168efb4d"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/ffdc844e673d2bcb2af8c8c3eef8cdea59d0bf32"
}
],
"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.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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