CVE-2026-89537

Estado: RecibidaCrítica (9.1)—

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

SUNRPC: Reject short RFC 4121 MIC tokens in gss_krb5_verify_mic_v2

gss_krb5_verify_mic_v2() reads the token ID at ptr[0..1], the flags byte at ptr[2], and padding at ptr[3..7], then passes ptr + GSS_KRB5_TOK_HDR_LEN and cksum_len to gss_krb5_mic_build_sg(). None of these accesses check read_token->len first.

The minimum safe token size is GSS_KRB5_TOK_HDR_LEN (16) plus ctx->krb5e->cksum_len (12-24, depending on the enctype). All callers accept shorter tokens from the wire:

Add a length guard at the top of gss_krb5_verify_mic_v2(), before any ptr[] access or scatterlist construction. Well-formed MIC tokens from gss_krb5_get_mic_v2() already have exactly GSS_KRB5_TOK_HDR_LEN + cksum_len bytes, so valid traffic is unaffected.

Detalles técnicos trazas, registros y código del informe original

 - gss_unwrap_resp_integ() enforces only an upper bound
   (offset + len <= rcv_buf->len) before allocating
   mic.data = kmalloc(len) and passing it to gss_verify_mic().
   A malicious NFS server can therefore supply a short checksum
   opaque, producing a small slab allocation that the Kerberos MIC
   verifier reads past.

 - gss_validate() enforces only len <= RPC_MAX_AUTH_SIZE (400)
   before passing the wire-supplied length to
   gss_validate_seqno_mic(), which constructs a mic xdr_netobj
   and calls gss_verify_mic().

 - svcauth_gss_verify_header() enforces only
   checksum.len >= XDR_UNIT (4 bytes) before dispatching to
   gss_verify_mic().

 - svcauth_gss_unwrap_integ() checks only that the checksum fits
   in gsd->gsd_scratch.

CVSS

Versión: 3.1
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Puntuación base: 9.1

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.54%
Percentil entre todas las CVEs puntuadas: 43
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 access85 %
Impacto principalT1499.004 Application or System Exploitationimpact75 %
Impacto secundarioT1005 Data from Local Systemcollection70 %

Vulnerabilidad remota en kernel Linux sin autenticación (AV:N/PR:N/UI:N) que permite DoS por lectura fuera de límites en tokens Kerberos MIC de NFS, accesible desde la red sin privilegios.

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 Application Isolation and Sandboxing

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-2026-89537",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 9.1,
          "attackVector": "NETWORK",
          "baseSeverity": "CRITICAL",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.2,
        "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": "de9c17eb4a912c9028f7b470eb80815144883b26",
              "lessThan": "7a946b2e7207f968902f2147ab9b30726f82f7ab",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "de9c17eb4a912c9028f7b470eb80815144883b26",
              "lessThan": "b94f6719dcd9f7a609bc5f459f85795900e77d25",
              "versionType": "git"
            }
          ],
          "programFiles": [
            "net/sunrpc/auth_gss/gss_krb5_unseal.c"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.35"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "2.6.35",
              "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": [
            "net/sunrpc/auth_gss/gss_krb5_unseal.c"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2026-09-11T20:19:36.733",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/7a946b2e7207f968902f2147ab9b30726f82f7ab",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/b94f6719dcd9f7a609bc5f459f85795900e77d25",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Received",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nSUNRPC: Reject short RFC 4121 MIC tokens in gss_krb5_verify_mic_v2\n\ngss_krb5_verify_mic_v2() reads the token ID at ptr[0..1], the flags\nbyte at ptr[2], and padding at ptr[3..7], then passes\nptr + GSS_KRB5_TOK_HDR_LEN and cksum_len to gss_krb5_mic_build_sg().\nNone of these accesses check read_token->len first.\n\nThe minimum safe token size is GSS_KRB5_TOK_HDR_LEN (16) plus\nctx->krb5e->cksum_len (12-24, depending on the enctype).  All callers\naccept shorter tokens from the wire:\n\n - gss_unwrap_resp_integ() enforces only an upper bound\n   (offset + len <= rcv_buf->len) before allocating\n   mic.data = kmalloc(len) and passing it to gss_verify_mic().\n   A malicious NFS server can therefore supply a short checksum\n   opaque, producing a small slab allocation that the Kerberos MIC\n   verifier reads past.\n\n - gss_validate() enforces only len <= RPC_MAX_AUTH_SIZE (400)\n   before passing the wire-supplied length to\n   gss_validate_seqno_mic(), which constructs a mic xdr_netobj\n   and calls gss_verify_mic().\n\n - svcauth_gss_verify_header() enforces only\n   checksum.len >= XDR_UNIT (4 bytes) before dispatching to\n   gss_verify_mic().\n\n - svcauth_gss_unwrap_integ() checks only that the checksum fits\n   in gsd->gsd_scratch.\n\nAdd a length guard at the top of gss_krb5_verify_mic_v2(), before any\nptr[] access or scatterlist construction.  Well-formed MIC tokens from\ngss_krb5_get_mic_v2() already have exactly GSS_KRB5_TOK_HDR_LEN +\ncksum_len bytes, so valid traffic is unaffected."
    }
  ],
  "lastModified": "2026-09-13T07:17:16.000",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}