CVE-2026-90036 (GCVE-0-2026-90036)

Vulnerability from cvelistv5 – Published: 2026-09-16 10:33 – Updated: 2026-10-21 12:49
VLAI
Title
NFSD: Prevent client use-after-free during blocked-lock reaping
Summary
In the Linux kernel, the following vulnerability has been resolved: NFSD: Prevent client use-after-free during blocked-lock reaping A bare lock owner -- its only remaining reference a blocked lock on nn->blocked_locks_lru -- holds a raw pointer to its nfs4_client but no reference keeping the client alive. When the per-net laundromat reaps such a lock, freeing the nbl drops the owner reference held through flc_owner, and the final nfs4_put_stateowner() takes the client's cl_lock. Because the laundromat detaches the nbl first, __destroy_client() no longer finds it, so a concurrent force_expire_client() can free the client before nfs4_put_stateowner() runs, dereferencing cl_lock in freed memory. Pin the client with cl_rpc_users before dropping nn->blocked_locks_lock, and skip clients already expiring, whose blocked locks __destroy_client() frees while holding an owner reference. Take nn->client_lock outside nn->blocked_locks_lock. Every other site holds nn->blocked_locks_lock as a leaf, acquiring no further lock, so placing nn->client_lock outside it cannot form a lock-order cycle.
Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 7018 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 7919d0a27f1e7cb324e023776aa1cbff00f1ee7b , < 0d53a47c913d0bce3b5ec35c28cbcca4d015f33d (git)
Affected: 7919d0a27f1e7cb324e023776aa1cbff00f1ee7b , < 7081224a59a0ca4edcd62c068588f4d900199a18 (git)
Affected: 7919d0a27f1e7cb324e023776aa1cbff00f1ee7b , < cd489b03587378645fe0d20142a33f1ed60bac98 (git)
Affected: 7919d0a27f1e7cb324e023776aa1cbff00f1ee7b , < 6fedb2eaff77554ca7a0deffd2e8bc0d6e8b38b0 (git)
Affected: 7919d0a27f1e7cb324e023776aa1cbff00f1ee7b , < 9026932ac8be4d0ae01db47f23619a98cc57b671 (git)
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Linux Linux Affected: 4.9
Unaffected: 0 , < 4.9 (semver)
Unaffected: 6.6.160 , ≤ 6.6.* (semver)
Unaffected: 6.12.111 , ≤ 6.12.* (semver)
Unaffected: 6.18.51 , ≤ 6.18.* (semver)
Unaffected: 7.2.5 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
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{
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      "affected": [
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/nfs4state.c"
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          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "version": "0",
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              "versionType": "semver"
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              "status": "unaffected",
              "version": "6.12.111",
              "versionType": "semver"
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            {
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              "status": "unaffected",
              "version": "6.18.51",
              "versionType": "semver"
            },
            {
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              "status": "unaffected",
              "version": "7.2.5",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
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        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.160",
                  "versionStartIncluding": "4.9",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.111",
                  "versionStartIncluding": "4.9",
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                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.51",
                  "versionStartIncluding": "4.9",
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                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nNFSD: Prevent client use-after-free during blocked-lock reaping\n\nA bare lock owner -- its only remaining reference a blocked lock on\nnn-\u003eblocked_locks_lru -- holds a raw pointer to its nfs4_client but\nno reference keeping the client alive. When the per-net laundromat\nreaps such a lock, freeing the nbl drops the owner reference\nheld through flc_owner, and the final nfs4_put_stateowner()\ntakes the client\u0027s cl_lock. Because the laundromat detaches the\nnbl first, __destroy_client() no longer finds it, so a concurrent\nforce_expire_client() can free the client before nfs4_put_stateowner()\nruns, dereferencing cl_lock in freed memory.\n\nPin the client with cl_rpc_users before dropping\nnn-\u003eblocked_locks_lock, and skip clients already expiring, whose\nblocked locks __destroy_client() frees while holding an owner\nreference. Take nn-\u003eclient_lock outside nn-\u003eblocked_locks_lock.\nEvery other site holds nn-\u003eblocked_locks_lock as a leaf, acquiring\nno further lock, so placing nn-\u003eclient_lock outside it cannot form\na lock-order cycle."
        }
      ],
      "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 - NFSD is the in-kernel NFS server; the UAF is reached by remote NFSv4.1 COMPOUND RPCs over TCP/UDP 2049 (EXCHANGE_ID, CREATE_SESSION, OPEN, blocking LOCK, DESTROY_SESSION, DESTROY_CLIENTID) that queue a blocked lock and expire the client while nfs4_laundromat() reaps it.\nAC:L - The attacker controls both sides: one client holds a conflicting lock while another queues a FILE_LOCK_DEFERRED blocked lock (bare lockowner), then DESTROY_CLIENTID races with laundromat free_blocked_lock() after nbl detach; concurrent compounds create the race and it is retryable.\nPR:N - Typical nfsd deployments use AUTH_SYS/AUTH_NULL with no cryptographic RPC authentication. A remote peer that can reach an export can create NFSv4.1 state and issue DESTROY_CLIENTID (ALLOWED_WITHOUT_FH) without a local account or kernel capabilities on the server.\nUI:N - Exploitation requires only attacker-sent NFS RPCs against a running nfsd export. No victim user action such as mounting a filesystem or opening a local file on the server is required.\nS:U - The use-after-free is of struct nfs4_client in the NFS server kernel and does not cross a separate security authority such as a VM, guest/host, sandbox, or IOMMU boundary.\nC:H - free_blocked_lock() drops flc_owner into nfs4_put_stateowner(), which takes cl_lock on a nfs4_client already freed by concurrent expire_client(). The mergeable client_slab object (KMEM_CACHE flags 0) can be reclaimed via EXCHANGE_ID to disclose kernel memory.\nI:H - nfs4_put_stateowner() does atomic_dec_and_lock on the freed client\u0027s cl_lock and so_unhash walks client-owned lists; reclaiming the nfs4_client slab enables heap corruption and control-flow hijack. Kernel guidance scores use-after-free as I:H.\nA:H - Use-after-free of nfs4_client (spin_lock of freed cl_lock) in the laundromat worker oopses or panics the NFS server even without full exploitation, fully denying service of the host."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-21T12:49:32.115Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/0d53a47c913d0bce3b5ec35c28cbcca4d015f33d"
        },
        {
          "url": "https://git.kernel.org/stable/c/7081224a59a0ca4edcd62c068588f4d900199a18"
        },
        {
          "url": "https://git.kernel.org/stable/c/cd489b03587378645fe0d20142a33f1ed60bac98"
        },
        {
          "url": "https://git.kernel.org/stable/c/6fedb2eaff77554ca7a0deffd2e8bc0d6e8b38b0"
        },
        {
          "url": "https://git.kernel.org/stable/c/9026932ac8be4d0ae01db47f23619a98cc57b671"
        }
      ],
      "title": "NFSD: Prevent client use-after-free during blocked-lock reaping",
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-90036",
    "datePublished": "2026-09-16T10:33:35.967Z",
    "dateReserved": "2026-09-11T19:38:34.782Z",
    "dateUpdated": "2026-10-21T12:49:32.115Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-90036",
      "date": "2026-11-01",
      "epss": "0.00484",
      "percentile": "0.41732"
    },
    "microsoft_vex": {
      "current_release_date": "2026-10-21T18:32:45.000Z",
      "cve": "CVE-2026-90036",
      "id": "msrc_CVE-2026-90036",
      "initial_release_date": "2026-09-17T01:08:09.000Z",
      "product_status:known_affected": "3",
      "product_status:under_investigation": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "NFSD: Prevent client use-after-free during blocked-lock reaping",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-90036.json",
      "version": "5"
    },
    "nvd": {
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                "product": "Linux",
                "programFiles": [
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                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
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                    "status": "affected",
                    "version": "4.9"
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        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nNFSD: Prevent client use-after-free during blocked-lock reaping\n\nA bare lock owner -- its only remaining reference a blocked lock on\nnn-\u003eblocked_locks_lru -- holds a raw pointer to its nfs4_client but\nno reference keeping the client alive. When the per-net laundromat\nreaps such a lock, freeing the nbl drops the owner reference\nheld through flc_owner, and the final nfs4_put_stateowner()\ntakes the client\u0027s cl_lock. Because the laundromat detaches the\nnbl first, __destroy_client() no longer finds it, so a concurrent\nforce_expire_client() can free the client before nfs4_put_stateowner()\nruns, dereferencing cl_lock in freed memory.\n\nPin the client with cl_rpc_users before dropping\nnn-\u003eblocked_locks_lock, and skip clients already expiring, whose\nblocked locks __destroy_client() frees while holding an owner\nreference. Take nn-\u003eclient_lock outside nn-\u003eblocked_locks_lock.\nEvery other site holds nn-\u003eblocked_locks_lock as a leaf, acquiring\nno further lock, so placing nn-\u003eclient_lock outside it cannot form\na lock-order cycle."
          }
        ],
        "id": "CVE-2026-90036",
        "lastModified": "2026-10-21T13:20:34.647",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "HIGH",
                "baseScore": 9.8,
                "baseSeverity": "CRITICAL",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "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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              "impactScore": 5.9,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
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        "published": "2026-09-16T11:17:16.803",
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            "url": "https://git.kernel.org/stable/c/0d53a47c913d0bce3b5ec35c28cbcca4d015f33d"
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          },
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            "url": "https://git.kernel.org/stable/c/7081224a59a0ca4edcd62c068588f4d900199a18"
          },
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            "url": "https://git.kernel.org/stable/c/9026932ac8be4d0ae01db47f23619a98cc57b671"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/cd489b03587378645fe0d20142a33f1ed60bac98"
          }
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        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-10-30T04:35:18+00:00",
      "cve": "CVE-2026-90036",
      "id": "CVE-2026-90036",
      "initial_release_date": "2026-09-16T00:00:00+00:00",
      "product_status:fixed": "777",
      "product_status:known_affected": "52",
      "product_status:under_investigation": "14",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: NFSD: Prevent client use-after-free during blocked-lock reaping",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-90036.json",
      "version": "3"
    }
  }
}



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