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CVE-2026-89689 (GCVE-0-2026-89689)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:46 – Updated: 2026-09-13 06:33
VLAI
Title
nfsd: don't free session slots that are still in use
Summary
In the Linux kernel, the following vulnerability has been resolved: nfsd: don't free session slots that are still in use nfsd4_sequence() can free the very slot it is currently processing. When the session shrinker has reduced se_target_maxslots below se_fchannel.maxreqs, the shrink path checks three conditions before calling free_session_slots(): 1. se_target_maxslots < maxreqs (shrink was advertised) 2. slot->sl_generation == se_slot_gen (slot is up-to-date) 3. seq->maxslots <= se_target_maxslots (client acknowledges) However, seq->slotid is never checked against se_target_maxslots. A client using a slot in the range [se_target_maxslots, maxreqs) can satisfy all three conditions: its slot has the current generation (set by a prior SEQUENCE), and it sends sa_highest_slotid <= se_target_maxslots to acknowledge the reduction. free_session_slots() then kfrees every slot at index >= se_target_maxslots, including the caller's own slot. The function continues to write sl_seqid, sl_flags, sl_generation, and stores the dangling pointer in cstate->slot. Later, nfsd4_store_cache_entry() copies up to maxresp_cached bytes of the compound reply into the freed sl_data[] array, corrupting whatever slab object now occupies that address. Additionally, a concurrent thread processing SEQUENCE on a different high-numbered slot can have its slot freed out from under it. NFSD4_SLOT_INUSE is set under nn->client_lock before the lock is released, so any concurrent thread past SEQUENCE will have its slot marked. However, free_session_slots() does not check NFSD4_SLOT_INUSE before freeing. Fix both problems by: 1. Checking that the current request's slotid is below the shrink boundary. 2. Scanning slots in the to-be-freed range for NFSD4_SLOT_INUSE and deferring the shrink if any are active.
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: fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 , < 72d40b103bb03f0124d3a3c8f71a30cbafaf6afa (git)
Affected: fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 , < b449b134e7762ddf98653a4b1d3e76d2d212ea64 (git)
Affected: fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 , < f5d22e372f4ac3eb287037a488c29691d52a6330 (git)
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Linux Linux Affected: 6.14
Unaffected: 0 , < 6.14 (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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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/nfs4state.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "lessThan": "72d40b103bb03f0124d3a3c8f71a30cbafaf6afa",
              "status": "affected",
              "version": "fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7",
              "versionType": "git"
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              "status": "affected",
              "version": "fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7",
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              "status": "affected",
              "version": "fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/nfs4state.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.14"
            },
            {
              "lessThan": "6.14",
              "status": "unaffected",
              "version": "0",
              "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"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.50",
                  "versionStartIncluding": "6.14",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.4",
                  "versionStartIncluding": "6.14",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3-rc1",
                  "versionStartIncluding": "6.14",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: don\u0027t free session slots that are still in use\n\nnfsd4_sequence() can free the very slot it is currently processing.\nWhen the session shrinker has reduced se_target_maxslots below\nse_fchannel.maxreqs, the shrink path checks three conditions before\ncalling free_session_slots():\n\n  1. se_target_maxslots \u003c maxreqs  (shrink was advertised)\n  2. slot-\u003esl_generation == se_slot_gen  (slot is up-to-date)\n  3. seq-\u003emaxslots \u003c= se_target_maxslots  (client acknowledges)\n\nHowever, seq-\u003eslotid is never checked against se_target_maxslots.\nA client using a slot in the range [se_target_maxslots, maxreqs) can\nsatisfy all three conditions: its slot has the current generation\n(set by a prior SEQUENCE), and it sends sa_highest_slotid \u003c=\nse_target_maxslots to acknowledge the reduction.\n\nfree_session_slots() then kfrees every slot at index \u003e=\nse_target_maxslots, including the caller\u0027s own slot. The function\ncontinues to write sl_seqid, sl_flags, sl_generation, and stores the\ndangling pointer in cstate-\u003eslot. Later, nfsd4_store_cache_entry()\ncopies up to maxresp_cached bytes of the compound reply into the freed\nsl_data[] array, corrupting whatever slab object now occupies that\naddress.\n\nAdditionally, a concurrent thread processing SEQUENCE on a different\nhigh-numbered slot can have its slot freed out from under it.\nNFSD4_SLOT_INUSE is set under nn-\u003eclient_lock before the lock is\nreleased, so any concurrent thread past SEQUENCE will have its slot\nmarked. However, free_session_slots() does not check NFSD4_SLOT_INUSE\nbefore freeing.\n\nFix both problems by:\n 1. Checking that the current request\u0027s slotid is below the shrink\n    boundary.\n 2. Scanning slots in the to-be-freed range for NFSD4_SLOT_INUSE and\n    deferring the shrink if any are active."
        }
      ],
      "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 bug is in nfsd4_sequence() in the in-kernel NFSv4.1 server (fs/nfsd/nfs4state.c). A remote client reaches it by sending COMPOUND RPCs with OP_SEQUENCE over TCP/2049 after EXCHANGE_ID/CREATE_SESSION; no local access to the NFS server is required.\nAC:L - After CREATE_SESSION with multiple slots, the attacker can grow the slot table and consume DRC memory so the nfsd-DRC-slot shrinker lowers se_target_maxslots, which SEQUENCE replies report. A SEQUENCE on a high slotid with sa_highest_slotid acknowledging the shrink then kfree\u0027s that in-use slot. Slotid, maxslots, cachethis, and concurrent COMPOUNDs are attacker-controlled.\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 and then SEQUENCE (ALLOWED_WITHOUT_FH, no filehandle or OPEN required); no local account or capability on the NFS server is needed.\nUI:N - The attacking NFS client sends the EXCHANGE_ID, CREATE_SESSION, and crafted SEQUENCE compounds itself. No victim user or administrator action on the NFS server, such as mounting an export or opening a file, is required.\nS:U - The use-after-free corrupts nfsd session-slot heap objects inside the NFS server host kernel. Impact stays in that kernel security authority and does not cross a VM, IOMMU, or sandbox boundary.\nC:H - free_session_slots() kfree\u0027s the nfsd4_slot still referenced by cstate-\u003eslot. Later nfsd4_store_cache_entry() and SEQUENCE processing read the freed object, including sl_cred. Slab reuse of the DRC slot (up to 2048-byte sl_data) enables arbitrary kernel memory disclosure per UAF guidance.\nI:H - After the kfree, nfsd4_sequence() writes sl_seqid, sl_flags, and sl_generation through the dangling pointer, and nfsd4_store_cache_entry() copies up to maxresp_cached bytes of the compound reply into freed sl_data[] and runs free_svc_cred() on reused memory, yielding a kernel heap write/arbitrary-free primitive.\nA:H - Use-after-free of the in-use session slot oopses or panics nfsd when the dangling cstate-\u003eslot is dereferenced or when concurrent SEQUENCE threads hit a freed slot. The attacker can repeat the SEQUENCE compounds to deny NFS service and take down the host."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-13T06:33:13.546Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/72d40b103bb03f0124d3a3c8f71a30cbafaf6afa"
        },
        {
          "url": "https://git.kernel.org/stable/c/b449b134e7762ddf98653a4b1d3e76d2d212ea64"
        },
        {
          "url": "https://git.kernel.org/stable/c/f5d22e372f4ac3eb287037a488c29691d52a6330"
        }
      ],
      "title": "nfsd: don\u0027t free session slots that are still in use",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89689",
    "datePublished": "2026-09-11T19:46:09.976Z",
    "dateReserved": "2026-09-11T19:38:34.749Z",
    "dateUpdated": "2026-09-13T06:33:13.546Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-89689",
      "date": "2026-09-16",
      "epss": "0.00605",
      "percentile": "0.47378"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-89689\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-09-11T20:19:55.900\",\"lastModified\":\"2026-09-13T07:17:34.723\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nnfsd: don\u0027t free session slots that are still in use\\n\\nnfsd4_sequence() can free the very slot it is currently processing.\\nWhen the session shrinker has reduced se_target_maxslots below\\nse_fchannel.maxreqs, the shrink path checks three conditions before\\ncalling free_session_slots():\\n\\n  1. se_target_maxslots \u003c maxreqs  (shrink was advertised)\\n  2. slot-\u003esl_generation == se_slot_gen  (slot is up-to-date)\\n  3. seq-\u003emaxslots \u003c= se_target_maxslots  (client acknowledges)\\n\\nHowever, seq-\u003eslotid is never checked against se_target_maxslots.\\nA client using a slot in the range [se_target_maxslots, maxreqs) can\\nsatisfy all three conditions: its slot has the current generation\\n(set by a prior SEQUENCE), and it sends sa_highest_slotid \u003c=\\nse_target_maxslots to acknowledge the reduction.\\n\\nfree_session_slots() then kfrees every slot at index \u003e=\\nse_target_maxslots, including the caller\u0027s own slot. The function\\ncontinues to write sl_seqid, sl_flags, sl_generation, and stores the\\ndangling pointer in cstate-\u003eslot. Later, nfsd4_store_cache_entry()\\ncopies up to maxresp_cached bytes of the compound reply into the freed\\nsl_data[] array, corrupting whatever slab object now occupies that\\naddress.\\n\\nAdditionally, a concurrent thread processing SEQUENCE on a different\\nhigh-numbered slot can have its slot freed out from under it.\\nNFSD4_SLOT_INUSE is set under nn-\u003eclient_lock before the lock is\\nreleased, so any concurrent thread past SEQUENCE will have its slot\\nmarked. However, free_session_slots() does not check NFSD4_SLOT_INUSE\\nbefore freeing.\\n\\nFix both problems by:\\n 1. Checking that the current request\u0027s slotid is below the shrink\\n    boundary.\\n 2. Scanning slots in the to-be-freed range for NFSD4_SLOT_INUSE and\\n    deferring the shrink if any are active.\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"fs/nfsd/nfs4state.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7\",\"lessThan\":\"72d40b103bb03f0124d3a3c8f71a30cbafaf6afa\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7\",\"lessThan\":\"b449b134e7762ddf98653a4b1d3e76d2d212ea64\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7\",\"lessThan\":\"f5d22e372f4ac3eb287037a488c29691d52a6330\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"fs/nfsd/nfs4state.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"6.14\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"6.14\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.18.50\",\"lessThanOrEqual\":\"6.18.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.2.4\",\"lessThanOrEqual\":\"7.2.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.3-rc1\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H\",\"baseScore\":9.8,\"baseSeverity\":\"CRITICAL\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"HIGH\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":3.9,\"impactScore\":5.9}]},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/72d40b103bb03f0124d3a3c8f71a30cbafaf6afa\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/b449b134e7762ddf98653a4b1d3e76d2d212ea64\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/f5d22e372f4ac3eb287037a488c29691d52a6330\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}",
    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-09-15T11:30:21+00:00",
      "cve": "CVE-2026-89689",
      "id": "CVE-2026-89689",
      "initial_release_date": "2026-09-11T00:00:00+00:00",
      "product_status:known_affected": "76",
      "product_status:known_not_affected": "186",
      "product_status:under_investigation": "14",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: nfsd: don\u0027t free session slots that are still in use",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89689.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-09-16T00:00:12Z",
      "cve": "CVE-2026-89689",
      "id": "CVE-2026-89689",
      "initial_release_date": "2026-09-15T00:56:56Z",
      "product_status:known_not_affected": "353",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89689",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89689.json",
      "version": "3"
    }
  }
}



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  • 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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