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CVE-2026-89660 (GCVE-0-2026-89660)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:45 – Updated: 2026-09-13 06:32
VLAI
Title
NFSD: Prevent client use-after-free during admin state revocation
Summary
In the Linux kernel, the following vulnerability has been resolved: NFSD: Prevent client use-after-free during admin state revocation A stateid holds only a bare pointer to its nfs4_client; a stateid reference does not pin it. The client survives only because __destroy_client() drains its stateids before free_client() runs. nfsd4_revoke_states() drops nn->client_lock across revoke_one_stid(), which dereferences the client to revoke a stateid and read clp->cl_minorversion. A teardown racing the dropped lock can free the client first. Pinning cl_rpc_users under client_lock blocks the DESTROY_CLIENTID and EXCHANGE_ID teardown, which refuses while cl_rpc_users is non-zero. force_expire_client() ignores it: once its wait for cl_rpc_users to reach zero has passed, a later pin goes unnoticed. Under client_lock, skip a client whose cl_time is already zero -- force_expire_client() clears it there before waiting -- otherwise pin cl_rpc_users before dropping the lock. The walk then either sees the expiry and skips, or pins in time for that wait to cover the revoke.
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: 1c13bf9f2e3cd5a59ef988c6c5a49fe0f02bcdfc , < 549bd9868e9d77b07ea94870940d64342829c6ad (git)
Affected: 1c13bf9f2e3cd5a59ef988c6c5a49fe0f02bcdfc , < bf1f948691523282cc4905bc6cd325e0c0b49e6a (git)
Affected: 1c13bf9f2e3cd5a59ef988c6c5a49fe0f02bcdfc , < e270e5a0778e5bff852c8862ce9576ce70359393 (git)
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Linux Linux Affected: 6.9
Unaffected: 0 , < 6.9 (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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          "product": "Linux",
          "programFiles": [
            "fs/nfsd/nfs4state.c"
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              "operator": "OR"
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nNFSD: Prevent client use-after-free during admin state revocation\n\nA stateid holds only a bare pointer to its nfs4_client; a stateid\nreference does not pin it.  The client survives only because\n__destroy_client() drains its stateids before free_client() runs.\n\nnfsd4_revoke_states() drops nn-\u003eclient_lock across revoke_one_stid(),\nwhich dereferences the client to revoke a stateid and read\nclp-\u003ecl_minorversion.  A teardown racing the dropped lock can free\nthe client first.\n\nPinning cl_rpc_users under client_lock blocks the DESTROY_CLIENTID and\nEXCHANGE_ID teardown, which refuses while cl_rpc_users is non-zero.\nforce_expire_client() ignores it: once its wait for cl_rpc_users to\nreach zero has passed, a later pin goes unnoticed.\n\nUnder client_lock, skip a client whose cl_time is already zero --\nforce_expire_client() clears it there before waiting -- otherwise pin\ncl_rpc_users before dropping the lock.  The walk then either sees the\nexpiry and skips, or pins in time for that wait to cover the revoke."
        }
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              "value": "AV:N - The UAF is in nfsd nfsd4_revoke_states(). A remote NFSv4 peer reaches the racing expire_client() over TCP/2049 via EXCHANGE_ID/CREATE_SESSION, SETCLIENTID_CONFIRM, or DESTROY_CLIENTID (ALLOWED_WITHOUT_FH), which free nfs4_client while the revoke walk still dereferences it.\nAC:L - The attacker controls the teardown side: they hold many stateids so the revoke walk drops client_lock once per stid, and concurrently retry EXCHANGE_ID/CREATE_SESSION or SETCLIENTID_CONFIRM so mark_client_expired_locked() succeeds while cl_rpc_users is unpinned.\nPR:N - EXCHANGE_ID, CREATE_SESSION, SETCLIENTID, SETCLIENTID_CONFIRM, and DESTROY_CLIENTID are ALLOWED_WITHOUT_FH with no export check. Typical AUTH_SYS/AUTH_NULL nfsd deployments do not verify RPC credentials, so any host that can reach TCP/2049 can establish state and trigger expire.\nUI:N - The attacker drives the NFS compounds that create state and expire the client. Administrative unlock_filesystem/unexport is a server operational condition (unexport or response to a misbehaving client), not a required victim user action.\nS:U - The freed object is struct nfs4_client in the NFS server kernel. Impact remains in that kernel security authority; there is no VM, IOMMU, or sandbox boundary crossing.\nC:H - revoke_one_stid() and the subsequent clp-\u003ecl_minorversion read dereference nfs4_client after free_client() kmem_cache_free\u0027s the mergeable client_slab object (KMEM_CACHE flags 0). Reclaim via EXCHANGE_ID discloses kernel memory; a UAF is C:H.\nI:H - revoke_one_stid() takes cl_lock and nfs4_put_stid() does refcount_dec_and_lock/idr_remove on the freed client\u0027s cl_lock/cl_stateids, concurrent with __destroy_client(), a slab UAF write primitive for heap corruption and control-flow hijacking.\nA:H - Use-after-free of nfs4_client in the nfsd revoke path oopses or panics the NFS server even without full exploitation, fully denying service of the host."
            }
          ]
        }
      ],
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        "dateUpdated": "2026-09-13T06:32:43.237Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/549bd9868e9d77b07ea94870940d64342829c6ad"
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          "url": "https://git.kernel.org/stable/c/bf1f948691523282cc4905bc6cd325e0c0b49e6a"
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89660",
    "datePublished": "2026-09-11T19:45:48.341Z",
    "dateReserved": "2026-09-11T19:38:34.744Z",
    "dateUpdated": "2026-09-13T06:32:43.237Z",
    "state": "PUBLISHED"
  },
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      "percentile": "0.46399"
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    "nvd": "{\"cve\":{\"id\":\"CVE-2026-89660\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-09-11T20:19:52.300\",\"lastModified\":\"2026-09-13T07:17:31.647\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nNFSD: Prevent client use-after-free during admin state revocation\\n\\nA stateid holds only a bare pointer to its nfs4_client; a stateid\\nreference does not pin it.  The client survives only because\\n__destroy_client() drains its stateids before free_client() runs.\\n\\nnfsd4_revoke_states() drops nn-\u003eclient_lock across revoke_one_stid(),\\nwhich dereferences the client to revoke a stateid and read\\nclp-\u003ecl_minorversion.  A teardown racing the dropped lock can free\\nthe client first.\\n\\nPinning cl_rpc_users under client_lock blocks the DESTROY_CLIENTID and\\nEXCHANGE_ID teardown, which refuses while cl_rpc_users is non-zero.\\nforce_expire_client() ignores it: once its wait for cl_rpc_users to\\nreach zero has passed, a later pin goes unnoticed.\\n\\nUnder client_lock, skip a client whose cl_time is already zero --\\nforce_expire_client() clears it there before waiting -- otherwise pin\\ncl_rpc_users before dropping the lock.  The walk then either sees the\\nexpiry and skips, or pins in time for that wait to cover the revoke.\"}],\"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\":\"1c13bf9f2e3cd5a59ef988c6c5a49fe0f02bcdfc\",\"lessThan\":\"549bd9868e9d77b07ea94870940d64342829c6ad\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1c13bf9f2e3cd5a59ef988c6c5a49fe0f02bcdfc\",\"lessThan\":\"bf1f948691523282cc4905bc6cd325e0c0b49e6a\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1c13bf9f2e3cd5a59ef988c6c5a49fe0f02bcdfc\",\"lessThan\":\"e270e5a0778e5bff852c8862ce9576ce70359393\",\"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\":\"6.9\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"6.9\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.18.51\",\"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/549bd9868e9d77b07ea94870940d64342829c6ad\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/bf1f948691523282cc4905bc6cd325e0c0b49e6a\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/e270e5a0778e5bff852c8862ce9576ce70359393\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}",
    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-09-13T06:51:25+00:00",
      "cve": "CVE-2026-89660",
      "id": "CVE-2026-89660",
      "initial_release_date": "2026-09-11T19:45:48.341000+00:00",
      "product_status:known_affected": "2",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: Linux kernel: NFSD use-after-free during client state revocation",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89660.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.

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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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