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CVE-2026-89659 (GCVE-0-2026-89659)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:45 – Updated: 2026-09-13 06:32
VLAI
Title
NFSD: Prevent client use-after-free during delegation revoke
Summary
In the Linux kernel, the following vulnerability has been resolved: NFSD: Prevent client use-after-free during delegation revoke A delegation stateid holds only a bare pointer to its owning nfs4_client and does not keep it alive. The client survives its stateids only because __destroy_client() drains cl_delegations and cl_revoked before free_client() runs. nfs4_laundromat() breaks that invariant: it unhashes an expired delegation from cl_delegations, drops deleg_lock, then revoke_delegation() relinks it onto cl_revoked under cl_lock. In that window the delegation is on neither list, so client_has_state() can report no remaining state. Every teardown path first requires cl_rpc_users to be zero, but the laundromat holds no such reference. A client whose recalled delegation has just timed out can therefore reach free_client() while revoke_delegation() is still about to dereference cl_lock, a use-after-free. Pin the client with cl_rpc_users across the revoke so teardown blocks until it completes, then reap the delegation from cl_revoked. A client already expiring reaps its own, so skip it and leave the delegation on del_recall_lru.
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: 3bd64a5ba1719c2bb6cba4493dfd3e23a7653e54 , < 3c0a53ee0b442348d8d2286d6960d3f07bb3a3d3 (git)
Affected: 3bd64a5ba1719c2bb6cba4493dfd3e23a7653e54 , < 2a9d637c2a8fd8ac29ad9b29f28d122ef75c1a56 (git)
Affected: 3bd64a5ba1719c2bb6cba4493dfd3e23a7653e54 , < 4683ca76b3b7e5808338491c6eb3c20e6b4894d5 (git)
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Linux Linux Affected: 3.10
Unaffected: 0 , < 3.10 (semver)
Unaffected: 6.18.51 , ≤ 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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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/netns.h",
            "fs/nfsd/nfs4state.c"
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          "vendor": "Linux",
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              "version": "3.10"
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              "version": "0",
              "versionType": "semver"
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              "status": "unaffected",
              "version": "6.18.51",
              "versionType": "semver"
            },
            {
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              "version": "7.2.4",
              "versionType": "semver"
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              "version": "7.3-rc1",
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                  "versionStartIncluding": "3.10",
                  "vulnerable": true
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nNFSD: Prevent client use-after-free during delegation revoke\n\nA delegation stateid holds only a bare pointer to its owning\nnfs4_client and does not keep it alive.  The client survives its\nstateids only because __destroy_client() drains cl_delegations and\ncl_revoked before free_client() runs.\n\nnfs4_laundromat() breaks that invariant: it unhashes an\nexpired delegation from cl_delegations, drops deleg_lock, then\nrevoke_delegation() relinks it onto cl_revoked under cl_lock.  In that\nwindow the delegation is on neither list, so client_has_state() can\nreport no remaining state.\n\nEvery teardown path first requires cl_rpc_users to be zero, but\nthe laundromat holds no such reference.  A client whose recalled\ndelegation has just timed out can therefore reach free_client()\nwhile revoke_delegation() is still about to dereference cl_lock,\na use-after-free.\n\nPin the client with cl_rpc_users across the revoke so teardown blocks\nuntil it completes, then reap the delegation from cl_revoked.  A client\nalready expiring reaps its own, so skip it and leave the delegation on\ndel_recall_lru."
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              "value": "AV:N - The bug is in nfsd nfs4_laundromat()/revoke_delegation() in fs/nfsd/nfs4state.c. A remote NFSv4 client reaches it over TCP/2049 by OPEN to obtain a delegation, a conflicting OPEN to force CB_RECALL, then DESTROY_CLIENTID or CREATE_SESSION replacement while the laundromat revokes.\nAC:L - The attacker controls both sides: it creates the recalled delegation, learns FATTR4_LEASE_TIME, and issues DESTROY_CLIENTID or same-name CREATE_SESSION/SETCLIENTID_CONFIRM while laundromat unhashes. Many recalled delegations widen the unhash-to-revoke window, and the sequence is retryable.\nPR:N - Default AUTH_SYS nfsd exports do no cryptographic authentication; any host allowed by the export ACL can EXCHANGE_ID/SETCLIENTID, OPEN to get a delegation, and DESTROY_CLIENTID. No local account or capability on the NFS server is required.\nUI:N - The attacking NFS client performs the full sequence itself (delegation, recall, teardown). No local user or administrator action on the NFS server is required at attack time.\nS:U - The use-after-free corrupts the nfs4_client object in the host kernel\u0027s nfsd state tables. Impact stays in that kernel security authority and does not cross a VM, IOMMU, or sandbox boundary.\nC:H - revoke_delegation() and nfs4_put_stid() dereference sc_client (cl_lock, cl_revoked, cl_stateids) after free_client() kmem_cache_free\u0027s the mergeable client_slab object (KMEM_CACHE flags 0), a UAF the attacker can reallocate via EXCHANGE_ID to disclose kernel memory.\nI:H - The UAF writes include spin_lock/unlock of freed cl_lock, list_add onto cl_revoked, and refcount_dec_and_lock in nfs4_put_stid on a reclaimable nfs4_client, enabling heap corruption and control-flow hijack.\nA:H - Use-after-free of nfs4_client in an nfsd/laundromat thread oopses or panics the NFS server even without full exploitation, and the attacker can repeat the RPC sequence to deny service."
            }
          ]
        }
      ],
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        "dateUpdated": "2026-09-13T06:32:42.114Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/4683ca76b3b7e5808338491c6eb3c20e6b4894d5"
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    "cveId": "CVE-2026-89659",
    "datePublished": "2026-09-11T19:45:47.587Z",
    "dateReserved": "2026-09-11T19:38:34.744Z",
    "dateUpdated": "2026-09-13T06:32:42.114Z",
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      "product_status:known_affected": "1",
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    "redhat_vex": {
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      "cve": "CVE-2026-89659",
      "id": "CVE-2026-89659",
      "initial_release_date": "2026-09-11T00:00:00+00:00",
      "product_status:known_affected": "262",
      "product_status:under_investigation": "14",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: NFSD: Prevent client use-after-free during delegation revoke",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89659.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-09-16T00:00:54Z",
      "cve": "CVE-2026-89659",
      "id": "CVE-2026-89659",
      "initial_release_date": "2026-09-12T16:24:06Z",
      "product_status:known_affected": "349",
      "product_status:known_not_affected": "4",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89659",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89659.json",
      "version": "4"
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  }
}



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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.


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