CVE-2026-89704

Estado: RecibidaAlta (7.5)—

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

nfsd: sample writeback error cursor before async COPY loop

_nfsd_copy_file_range() samples dst->f_wb_err into "since" after the copy loop, then uses it to detect writeback errors via filemap_check_wb_err() once vfs_fsync_range() returns. Because the nfsd_file cache reuses a single struct file across requests targeting the same inode, a concurrent COMMIT or stable WRITE on dst advances dst->f_wb_err to the current mapping->wb_err via file_check_and_advance_wb_err() during its own vfs_fsync_range().

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If that advancement lands between the writeback error appearing in mapping->wb_err and the COPY worker sampling "since", the worker captures the already-advanced cursor, errseq_check() sees cur == since and returns zero, and NFSD4_COPY_F_COMMITTED is set even though writeback failed. CB_OFFLOAD then encodes wr_stable_how = FILE_SYNC4, the client treats the copied data as durable, and the failure becomes silent data loss.

Sample since once at the start of the function. The cursor then reflects state in effect before this COPY issues any writes, and filemap_check_wb_err() detects any error that occurs during the copy regardless of which thread first observes it. This matches the pattern used by nfsd_vfs_write() and nfsd4_clone_file_range().

CVSS

Versión: 3.1
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Puntuación base: 7.5

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.53%
Percentil entre todas las CVEs puntuadas: 43
Fecha de la puntuación: 5/10/2026

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 principalT1565.001 Stored Data Manipulationimpact80 %
Impacto secundarioT1499.004 Application or System Exploitationimpact35 %

Vulnerabilidad en nfsd kernel que permite manipular errores de sincronización de archivos vía solicitudes COPY remotas (AV:N, PR:N, UI:N), causando pérdida silenciosa de datos (I:H). Afecta integridad y disponibilidad.

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-2026-89704",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 7.5,
          "attackVector": "NETWORK",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "NONE",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 3.6,
        "exploitabilityScore": 3.9
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  "published": "2026-09-11T20:19:57.657",
  "references": [
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Received",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: sample writeback error cursor before async COPY loop\n\n_nfsd_copy_file_range() samples dst->f_wb_err into \"since\"\nafter the copy loop, then uses it to detect writeback errors\nvia filemap_check_wb_err() once vfs_fsync_range() returns.\nBecause the nfsd_file cache reuses a single struct file\nacross requests targeting the same inode, a concurrent\nCOMMIT or stable WRITE on dst advances dst->f_wb_err to the\ncurrent mapping->wb_err via file_check_and_advance_wb_err()\nduring its own vfs_fsync_range(). If that advancement lands\nbetween the writeback error appearing in mapping->wb_err\nand the COPY worker sampling \"since\", the worker captures\nthe already-advanced cursor, errseq_check() sees cur ==\nsince and returns zero, and NFSD4_COPY_F_COMMITTED is set\neven though writeback failed. CB_OFFLOAD then encodes\nwr_stable_how = FILE_SYNC4, the client treats the copied\ndata as durable, and the failure becomes silent data loss.\n\nSample since once at the start of the function. The cursor\nthen reflects state in effect before this COPY issues any\nwrites, and filemap_check_wb_err() detects any error that\noccurs during the copy regardless of which thread first\nobserves it. This matches the pattern used by\nnfsd_vfs_write() and nfsd4_clone_file_range()."
    }
  ],
  "lastModified": "2026-09-14T13:19:20.367",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}