CVE-2026-89678

Estado: RecibidaAlta (7.5)—

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

nfsd: fix partial-write detection in nfsd_direct_write

nfsd_direct_write() walks a list of write segments and, after each vfs_iocb_iter_write(), tries to detect a short write so the loop can stop before placing the next segment at a wrong file offset:

vfs_iocb_iter_write() runs the iter through ->write_iter(), which advances the iter by the number of bytes written. By the time the check runs, segments[i].iter.count is the residual, not the original request length:

The condition then reduces to host_err < original_len - host_err, so the break fires only when less than half of the segment was written.

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Any short write completing between 50% and 99% of the segment slips through; the loop advances to the next segment with kiocb->ki_pos only bumped by the short amount, writing the next segment's payload at the wrong offset and over-reporting *cnt to the NFS client.

Snapshot the segment's byte count before the write and compare host_err against that snapshot so any short write breaks the loop.

Detalles técnicos trazas, registros y código del informe original

    host_err = vfs_iocb_iter_write(file, kiocb, &segments[i].iter);
    if (host_err < 0)
            return host_err;
    *cnt += host_err;
    if (host_err < segments[i].iter.count)
            break;	/* partial write */

    before write_iter: iter.count == original_len
    after  write_iter: iter.count == original_len - host_err

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: 0.38%
Percentil entre todas las CVEs puntuadas: 30
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 access75 %
Impacto principalT1565.002 Transmitted Data Manipulationimpact85 %
Impacto secundarioT1499.004 Application or System Exploitationimpact60 %

Vulnerabilidad remota sin autenticación en kernel Linux (AV:N/PR:N) que permite corrupción de datos en escrituras NFS parciales y denegación de servicio al sobrescribir archivos con contenido desalineado.

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 Privileged Account Management Network Segmentation Limit Access to Resource Over Network Encrypt Sensitive Information

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)

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{
  "id": "CVE-2026-89678",
  "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
      }
    ]
  },
  "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": "06c5c97293e3fca99ce15da157068edf45a7c6e4",
              "lessThan": "fa6590dfd16ab55f03b658b079072ace3504825e",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "06c5c97293e3fca99ce15da157068edf45a7c6e4",
              "lessThan": "250ec14932d5cfe102f68a57892bb566eee7f83e",
              "versionType": "git"
            }
          ],
          "programFiles": [
            "fs/nfsd/vfs.c"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.19"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "6.19",
              "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/vfs.c"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2026-09-11T20:19:54.523",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/250ec14932d5cfe102f68a57892bb566eee7f83e",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/fa6590dfd16ab55f03b658b079072ace3504825e",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Received",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: fix partial-write detection in nfsd_direct_write\n\nnfsd_direct_write() walks a list of write segments and, after each\nvfs_iocb_iter_write(), tries to detect a short write so the loop can\nstop before placing the next segment at a wrong file offset:\n\n    host_err = vfs_iocb_iter_write(file, kiocb, &segments[i].iter);\n    if (host_err < 0)\n            return host_err;\n    *cnt += host_err;\n    if (host_err < segments[i].iter.count)\n            break;\t/* partial write */\n\nvfs_iocb_iter_write() runs the iter through ->write_iter(), which\nadvances the iter by the number of bytes written. By the time the\ncheck runs, segments[i].iter.count is the residual, not the original\nrequest length:\n\n    before write_iter: iter.count == original_len\n    after  write_iter: iter.count == original_len - host_err\n\nThe condition then reduces to host_err < original_len - host_err, so\nthe break fires only when less than half of the segment was written.\nAny short write completing between 50% and 99% of the segment slips\nthrough; the loop advances to the next segment with kiocb->ki_pos\nonly bumped by the short amount, writing the next segment's payload\nat the wrong offset and over-reporting *cnt to the NFS client.\n\nSnapshot the segment's byte count before the write and compare\nhost_err against that snapshot so any short write breaks the loop."
    }
  ],
  "lastModified": "2026-09-13T07:17:33.533",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}