CVE-2026-89686 (GCVE-0-2026-89686)
Vulnerability from cvelistv5 – Published: 2026-09-11 19:46 – Updated: 2026-10-30 12:32
VLAI
EPSS
VEX
Title
nfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing delegation revoke
Summary
In the Linux kernel, the following vulnerability has been resolved:
nfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing delegation revoke
nfsd4_alloc_layout_stateid reads fp->fi_deleg_file without holding
fi_lock when the parent stateid is a delegation. A concurrent delegation
revoke via the laundromat can clear fi_deleg_file under fi_lock, causing
nfsd_file_get() to return NULL and triggering the BUG_ON.
This race is client-reachable: two NFS clients can trigger it by having
one hold a delegation while another opens the same file to force a
recall. When the first client doesn't respond to the recall, the
laundromat revokes it. A concurrent LAYOUTGET from any client using the
delegation stateid hits the race window.
Fix this by taking fi_lock around the fi_deleg_file read in the
SC_TYPE_DELEG path, matching the locking discipline of the
find_any_file() arm, and replacing the BUG_ON with a graceful error
return that cleans up the partially-initialized layout stateid.
Severity
9.8 (Critical)
SSVC
Exploitation: none
Automatable: yes
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-16 19:26 UTC
Assigner
References
6 references
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
c5c707f96fc9a6e5a57ca5baac892673270abe3d , < f5011c26246d1abed3dc750c9744e33cb79ff9bc
(git)
Affected: c5c707f96fc9a6e5a57ca5baac892673270abe3d , < d12af460df27876661707efab3a8532146cb961f (git) Affected: c5c707f96fc9a6e5a57ca5baac892673270abe3d , < c517f27498757e616d2a8fe6d16caad1fee422e6 (git) Affected: c5c707f96fc9a6e5a57ca5baac892673270abe3d , < 607a56fea772c1f4f4989d8e255dd4f7192d9604 (git) Affected: c5c707f96fc9a6e5a57ca5baac892673270abe3d , < 97bda8b4284d90897a1f1922e5082ff9e35d7c7e (git) Affected: c5c707f96fc9a6e5a57ca5baac892673270abe3d , < ca94ba36172046be6a694a7986f6931e47ed4d51 (git) |
guessed | |
| Linux | Linux |
Affected:
4.0
Unaffected: 0 , < 4.0 (semver) Unaffected: 6.1.191 , ≤ 6.1.* (semver) Unaffected: 6.6.160 , ≤ 6.6.* (semver) Unaffected: 6.12.109 , ≤ 6.12.* (semver) Unaffected: 6.18.50 , ≤ 6.18.* (semver) Unaffected: 7.2.4 , ≤ 7.2.* (semver) Unaffected: 7.3 , ≤ * (original_commit_for_fix) |
guessed |
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"status": "affected",
"version": "c5c707f96fc9a6e5a57ca5baac892673270abe3d",
"versionType": "git"
},
{
"lessThan": "607a56fea772c1f4f4989d8e255dd4f7192d9604",
"status": "affected",
"version": "c5c707f96fc9a6e5a57ca5baac892673270abe3d",
"versionType": "git"
},
{
"lessThan": "97bda8b4284d90897a1f1922e5082ff9e35d7c7e",
"status": "affected",
"version": "c5c707f96fc9a6e5a57ca5baac892673270abe3d",
"versionType": "git"
},
{
"lessThan": "ca94ba36172046be6a694a7986f6931e47ed4d51",
"status": "affected",
"version": "c5c707f96fc9a6e5a57ca5baac892673270abe3d",
"versionType": "git"
}
]
},
{
"defaultStatus": "affected",
"product": "Linux",
"programFiles": [
"fs/nfsd/nfs4layouts.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "4.0"
},
{
"lessThan": "4.0",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"version": "6.6.160",
"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",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.6.160",
"versionStartIncluding": "4.0",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.12.109",
"versionStartIncluding": "4.0",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.18.50",
"versionStartIncluding": "4.0",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "7.2.4",
"versionStartIncluding": "4.0",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "7.3",
"versionStartIncluding": "4.0",
"vulnerable": true
}
],
"negate": false,
"operator": "OR"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing delegation revoke\n\nnfsd4_alloc_layout_stateid reads fp-\u003efi_deleg_file without holding\nfi_lock when the parent stateid is a delegation. A concurrent delegation\nrevoke via the laundromat can clear fi_deleg_file under fi_lock, causing\nnfsd_file_get() to return NULL and triggering the BUG_ON.\n\nThis race is client-reachable: two NFS clients can trigger it by having\none hold a delegation while another opens the same file to force a\nrecall. When the first client doesn\u0027t respond to the recall, the\nlaundromat revokes it. A concurrent LAYOUTGET from any client using the\ndelegation stateid hits the race window.\n\nFix this by taking fi_lock around the fi_deleg_file read in the\nSC_TYPE_DELEG path, matching the locking discipline of the\nfind_any_file() arm, and replacing the BUG_ON with a graceful error\nreturn that cleans up the partially-initialized layout stateid."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 9.8,
"baseSeverity": "CRITICAL",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:N - The flaw is in nfsd pNFS LAYOUTGET (nfsd4_alloc_layout_stateid in fs/nfsd/nfs4layouts.c). A remote NFSv4.1 client reaches it over TCP/2049 via nfsd_dispatch to nfsd4_proc_compound to nfsd4_layoutget, so no local access to the NFS server is required.\nAC:L - The attacker controls both sides of the race: one NFS client obtains a delegation while another OPENs the same file to force recall, then the first client withholds CB_RECALL and issues concurrent LAYOUTGET with the delegation stateid as the laundromat runs put_deleg_file. The sequence is retryable and can be timed using FATTR4_LEASE_TIME.\nPR:N - Typical nfsd deployments accept AUTH_SYS/AUTH_NULL without cryptographic authentication. Any host allowed by the export ACL can EXCHANGE_ID/CREATE_SESSION, OPEN to receive a delegation, and LAYOUTGET; no local account or capability on the NFS server is required.\nUI:N - The attacking NFS clients drive the OPEN, recall, and LAYOUTGET compounds themselves against an already-running nfsd export. No victim user action such as mounting a filesystem or opening a file on the server is required.\nS:U - The unlocked fi_deleg_file load and resulting BUG_ON or nfsd_file use-after-free occur in kernel nfsd state on the NFS server host. Impact stays in that kernel security authority and does not cross a VM, IOMMU, or sandbox boundary.\nC:H - put_deleg_file may drop the last nfsd_file ref and call_rcu-free it (KMEM_CACHE flags 0, not SLAB_TYPESAFE_BY_RCU) while LAYOUTGET still calls nfsd_file_get on the stale pointer. After slab reuse the layout stateid\u0027s nf_file can be leveraged for kernel information disclosure.\nI:H - The same stale nfsd_file pointer is used for refcount_inc_not_zero and later nfsd4_layout_setlease/kernel_setlease on nf_file. Heap reuse of the nfsd_file slab enables an arbitrary write or control-flow hijack per kernel UAF scoring guidance.\nA:H - When nfsd_file_get returns NULL the original code hits BUG_ON(!ls-\u003els_file), oopsing or panicking the nfsd thread. Even without that assertion, use-after-free of nfsd_file crashes nfsd, and the attacker can repeat LAYOUTGET to deny NFS service."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-10-21T12:48:21.196Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/d12af460df27876661707efab3a8532146cb961f"
},
{
"url": "https://git.kernel.org/stable/c/c517f27498757e616d2a8fe6d16caad1fee422e6"
},
{
"url": "https://git.kernel.org/stable/c/607a56fea772c1f4f4989d8e255dd4f7192d9604"
},
{
"url": "https://git.kernel.org/stable/c/97bda8b4284d90897a1f1922e5082ff9e35d7c7e"
},
{
"url": "https://git.kernel.org/stable/c/ca94ba36172046be6a694a7986f6931e47ed4d51"
}
],
"title": "nfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing delegation revoke",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-89686",
"datePublished": "2026-09-11T19:46:07.877Z",
"dateReserved": "2026-09-11T19:38:34.749Z",
"dateUpdated": "2026-10-21T12:48:21.196Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
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Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
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.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
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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.