CVE-2026-93221

Estado: RecibidaAlta (8.1)—

In the Linux kernel, the following vulnerability has been resolved:

nfsd: convert nfsd_net boolean flags to unsigned long flags word

nfsd_net contains several boolean fields that are accessed from concurrent contexts without serialization. In particular, nfsd4_end_grace() guards its drain path with a plain bool:

The read and the write are independent, and nothing in struct nfsd_net serializes them. At least two contexts can reach this code with no lock held:

Both callers can observe grace_ended == false on different CPUs, both store true, and both proceed into nfsd4_record_grace_done(), which invokes the active client_tracking_ops->grace_done callback.

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For tracking ops that drain reclaim_str_hashtbl (legacy_tracking_ops via nfsd4_recdir_purge_old, and the cld v1+ ops via nfsd4_cld_grace_done), grace_done calls nfs4_release_reclaim(), which walks every bucket of reclaim_str_hashtbl with no lock and calls nfs4_remove_reclaim_record() (list_del + kfree) on each entry. Two concurrent walkers corrupt the list and double-free every nfs4_client_reclaim. A concurrent nfsd4_find_reclaim_client() iterating the same bucket reads through freed memory.

A third call site exists in nfs4_state_start_net() on the skip_grace startup path, but it runs under nfsd_mutex before any client has connected and before the laundromat's first delayed work fires, so it cannot race with the two callers above.

Replace the scattered boolean fields in nfsd_net with a single unsigned long flags word and an enum nfsd_net_flag for the bit positions. The grace_ended race is fixed by using test_and_set_bit(), which is atomic on all architectures. The remaining flags (grace_end_forced, in_grace, somebody_reclaimed, track_reclaim_completes, nfsd_net_up, lockd_up) are converted to use test_bit/set_bit/clear_bit for consistency. This avoids sub-word cmpxchg issues on architectures like Hexagon that only support word-sized atomic operations.

Detalles técnicos trazas, registros y código del informe original

    if (nn->grace_ended)
            return;
    nn->grace_ended = true;

    laundromat path
      laundry_wq kworker
        nfs4_laundromat()
          nfsd4_end_grace()

    RECLAIM_COMPLETE path
      nfsd compound kthread
        nfsd4_reclaim_complete()
          inc_reclaim_complete()
            nfsd4_end_grace()

CVSS

Versión: 3.1
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Puntuación base: 8.1

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.33%
Percentil entre todas las CVEs puntuadas: 24
Fecha de la puntuación: 6/10/2026

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

ExplotaciónT1190 Exploit Public-Facing Applicationinitial access45 %
Impacto principalT1499.004 Application or System Exploitationimpact70 %
Impacto secundarioT1565.001 Stored Data Manipulationimpact55 %

Vulnerabilidad de race condition en kernel Linux (AV:N) sin autenticación requerida que causa corrupción de memoria y DoS; remotamente explotable en contextos NFS con acceso de red sin privilegios previos.

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Filter Network Traffic Vulnerability Scanning Restrict File and Directory Permissions Privileged Account Management Remote Data Storage Network Segmentation

Tecnologías afectadas (1)

⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.

Linux — Linux Kernel^AI

Referencias

JSON original (NVD)

Mostrar

{
  "id": "CVE-2026-93221",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 8.1,
          "attackVector": "NETWORK",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "HIGH",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 2.2
      }
    ]
  },
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "362063a595be959bc08f4163e6405a0266740091",
              "lessThan": "df5922fe09a8131c793ffa86adf204999b0470f8",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "362063a595be959bc08f4163e6405a0266740091",
              "lessThan": "11a5fe42e1811f793e04ef885b639ea7668f439d",
              "versionType": "git"
            }
          ],
          "programFiles": [
            "fs/nfsd/netns.h",
            "fs/nfsd/nfs4proc.c",
            "fs/nfsd/nfs4recover.c",
            "fs/nfsd/nfs4state.c",
            "fs/nfsd/nfsctl.c",
            "fs/nfsd/nfssvc.c"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.2"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "5.2",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "7.2.4",
              "versionType": "semver",
              "lessThanOrEqual": "7.2.*"
            },
            {
              "status": "unaffected",
              "version": "7.3-rc1",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "fs/nfsd/netns.h",
            "fs/nfsd/nfs4proc.c",
            "fs/nfsd/nfs4recover.c",
            "fs/nfsd/nfs4state.c",
            "fs/nfsd/nfsctl.c",
            "fs/nfsd/nfssvc.c"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2026-09-24T16:17:17.310",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/11a5fe42e1811f793e04ef885b639ea7668f439d",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/df5922fe09a8131c793ffa86adf204999b0470f8",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Received",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: convert nfsd_net boolean flags to unsigned long flags word\n\nnfsd_net contains several boolean fields that are accessed from\nconcurrent contexts without serialization.  In particular,\nnfsd4_end_grace() guards its drain path with a plain bool:\n\n    if (nn->grace_ended)\n            return;\n    nn->grace_ended = true;\n\nThe read and the write are independent, and nothing in struct\nnfsd_net serializes them.  At least two contexts can reach this\ncode with no lock held:\n\n    laundromat path\n      laundry_wq kworker\n        nfs4_laundromat()\n          nfsd4_end_grace()\n\n    RECLAIM_COMPLETE path\n      nfsd compound kthread\n        nfsd4_reclaim_complete()\n          inc_reclaim_complete()\n            nfsd4_end_grace()\n\nBoth callers can observe grace_ended == false on different CPUs,\nboth store true, and both proceed into nfsd4_record_grace_done(),\nwhich invokes the active client_tracking_ops->grace_done callback.\nFor tracking ops that drain reclaim_str_hashtbl (legacy_tracking_ops\nvia nfsd4_recdir_purge_old, and the cld v1+ ops via\nnfsd4_cld_grace_done), grace_done calls nfs4_release_reclaim(),\nwhich walks every bucket of reclaim_str_hashtbl with no lock and\ncalls nfs4_remove_reclaim_record() (list_del + kfree) on each\nentry.  Two concurrent walkers corrupt the list and double-free\nevery nfs4_client_reclaim.  A concurrent nfsd4_find_reclaim_client()\niterating the same bucket reads through freed memory.\n\nA third call site exists in nfs4_state_start_net() on the\nskip_grace startup path, but it runs under nfsd_mutex before any\nclient has connected and before the laundromat's first delayed\nwork fires, so it cannot race with the two callers above.\n\nReplace the scattered boolean fields in nfsd_net with a single\nunsigned long flags word and an enum nfsd_net_flag for the bit\npositions.  The grace_ended race is fixed by using\ntest_and_set_bit(), which is atomic on all architectures.  The\nremaining flags (grace_end_forced, in_grace, somebody_reclaimed,\ntrack_reclaim_completes, nfsd_net_up, lockd_up) are converted to\nuse test_bit/set_bit/clear_bit for consistency.  This avoids\nsub-word cmpxchg issues on architectures like Hexagon that only\nsupport word-sized atomic operations."
    }
  ],
  "lastModified": "2026-09-25T05:17:00.150",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}