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CVE-2026-89686 (GCVE-0-2026-89686)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:46 – Updated: 2026-09-13 06:33
VLAI
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)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: c5c707f96fc9a6e5a57ca5baac892673270abe3d , < c517f27498757e616d2a8fe6d16caad1fee422e6 (git)
Affected: c5c707f96fc9a6e5a57ca5baac892673270abe3d , < 607a56fea772c1f4f4989d8e255dd4f7192d9604 (git)
Affected: c5c707f96fc9a6e5a57ca5baac892673270abe3d , < 97bda8b4284d90897a1f1922e5082ff9e35d7c7e (git)
Affected: c5c707f96fc9a6e5a57ca5baac892673270abe3d , < ca94ba36172046be6a694a7986f6931e47ed4d51 (git)
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Linux Linux Affected: 4.0
Unaffected: 0 , < 4.0 (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-rc1 , ≤ * (original_commit_for_fix)
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{
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      "affected": [
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          "product": "Linux",
          "programFiles": [
            "fs/nfsd/nfs4layouts.c"
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          "vendor": "Linux",
          "versions": [
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              "version": "4.0"
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
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              "versionType": "semver"
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              "versionType": "semver"
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              "version": "7.2.4",
              "versionType": "semver"
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              "status": "unaffected",
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              "versionType": "original_commit_for_fix"
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        }
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                  "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
                },
                {
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              "negate": false,
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        {
          "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": [
        {
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            "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"
          },
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              "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": "2026-09-13T06:33:09.795Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/c517f27498757e616d2a8fe6d16caad1fee422e6"
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          "url": "https://git.kernel.org/stable/c/607a56fea772c1f4f4989d8e255dd4f7192d9604"
        },
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          "url": "https://git.kernel.org/stable/c/97bda8b4284d90897a1f1922e5082ff9e35d7c7e"
        },
        {
          "url": "https://git.kernel.org/stable/c/ca94ba36172046be6a694a7986f6931e47ed4d51"
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      "title": "nfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing delegation revoke",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89686",
    "datePublished": "2026-09-11T19:46:07.877Z",
    "dateReserved": "2026-09-11T19:38:34.749Z",
    "dateUpdated": "2026-09-13T06:33:09.795Z",
    "state": "PUBLISHED"
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      "date": "2026-09-15",
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      "cve": "CVE-2026-89686",
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      "product_status:known_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "nfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing delegation revoke",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-89686.json",
      "version": "2"
    },
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    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-09-13T06:51:58+00:00",
      "cve": "CVE-2026-89686",
      "id": "CVE-2026-89686",
      "initial_release_date": "2026-09-11T19:46:07.877000+00:00",
      "product_status:known_affected": "2",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: Linux kernel (nfsd): Denial of Service due to a race condition in NFSv4 delegation revoke",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89686.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-16T00:00:16Z",
      "cve": "CVE-2026-89686",
      "id": "CVE-2026-89686",
      "initial_release_date": "2026-09-15T00:57:02Z",
      "product_status:known_affected": "349",
      "product_status:known_not_affected": "4",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89686",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89686.json",
      "version": "3"
    }
  }
}



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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

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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.


Detection rules are retrieved from Rulezet.