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CVE-2026-89542

Estado: RecibidaCrítica (9.8)—

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

SUNRPC: harden gss_krb5_unwrap_v2 against short tokens

gss_krb5_unwrap_v2() reads the EC and RRC header fields at ptr+4 and ptr+6 before validating that the token is at least GSS_KRB5_TOK_HDR_LEN (16) bytes long, and its rotate_left() helper passes buf->len - base to xdr_buf_subsegment() without verifying that base <= buf->len. When a caller hands in a sub-16-byte token, or a token whose declared len leaves base past the end of the buffer, three distinct failures follow:

After decryption, the cleanup arithmetic has the same shape:

Leer descripción completaMostrar menos

The BUG_ON re-adds the value just subtracted, so it reduces to min(A, B) > A and is permanently false; it cannot catch the unsigned underflow of movelen, which then drives a ~UINT_MAX-byte memmove().

Add four defense-in-depth guards inside the unwrap core so it is safe regardless of what its callers validate:

Detalles técnicos trazas, registros y código del informe original
    gss_krb5_unwrap_v2(offset, len, buf)
      ptr = buf->head[0].iov_base + offset
      ec  = *(ptr + 4)              /* OOB read on short head */
      rrc = *(ptr + 6)              /* OOB read on short head */
      rotate_left(offset + 16, buf, rrc)
        xdr_buf_subsegment(buf, &subbuf,
                           base, buf->len - base)   /* u32 wrap when base > len */
        _rotate_left(&subbuf, shift)
          shift %= buf->len         /* divide-by-zero when base == len */

    movelen = min_t(unsigned int, buf->head[0].iov_len, len);
    movelen -= offset + GSS_KRB5_TOK_HDR_LEN + headskip;
    BUG_ON(offset + GSS_KRB5_TOK_HDR_LEN + headskip + movelen >
                                            buf->head[0].iov_len);

  - reject tokens with len - offset < GSS_KRB5_TOK_HDR_LEN before
    touching ptr+4/ptr+6;
  - bail from rotate_left() when buf->len <= base, covering both the
    underflow and zero-length cases;
  - return early from _rotate_left() when buf->len is zero, so the
    shift %= buf->len modulo cannot fault;
  - replace the dead BUG_ON with a live check that returns
    GSS_S_DEFECTIVE_TOKEN before the movelen subtraction.

CVSS

Probabilidad de explotación (EPSS)

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.

Red sin privilegios (AV:N, PR:N, UI:N, CVSS crítico). OOB read y underflow en unwrap de GSS-KRB5 del kernel causan DoS (divide-by-zero, BUG_ON, memmove ~UINT_MAX) y potencialmente ejecución de código en contexto del kernel.

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

Privileged Account ManagementFilter Network TrafficVulnerability ScanningRestrict Web-Based ContentNetwork SegmentationLimit Software Installation

Tecnologías afectadas (1)

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

Linux — Linux KernelAI

Referencias

JSON original (NVD)

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{
  "id": "CVE-2026-89542",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 9.8,
          "attackVector": "NETWORK",
          "baseSeverity": "CRITICAL",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "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": "299d281c7225ded15b28cb861a98d818d82787fc",
              "versionType": "git"
            },
            {
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              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "de9c17eb4a912c9028f7b470eb80815144883b26",
              "lessThan": "075d7cfc4df8c54cb202ba8b28420370c03ba9b6",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "de9c17eb4a912c9028f7b470eb80815144883b26",
              "lessThan": "f2591660e0eb263c9415bf0d0bb1b111e62df7a4",
              "versionType": "git"
            },
            {
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              "lessThan": "dddcb0f4b7e27fac16a78ea9a1c8ec2e8a241087",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "de9c17eb4a912c9028f7b470eb80815144883b26",
              "lessThan": "806584a4b67a7233870c33e5b8f872e76dd02988",
              "versionType": "git"
            },
            {
              "status": "affected",
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            {
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              "versionType": "git"
            }
          ],
          "programFiles": [
            "net/sunrpc/auth_gss/gss_krb5_wrap.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": "5.10.270",
              "versionType": "semver",
              "lessThanOrEqual": "5.10.*"
            },
            {
              "status": "unaffected",
              "version": "5.15.221",
              "versionType": "semver",
              "lessThanOrEqual": "5.15.*"
            },
            {
              "status": "unaffected",
              "version": "6.1.188",
              "versionType": "semver",
              "lessThanOrEqual": "6.1.*"
            },
            {
              "status": "unaffected",
              "version": "6.6.157",
              "versionType": "semver",
              "lessThanOrEqual": "6.6.*"
            },
            {
              "status": "unaffected",
              "version": "6.12.109",
              "versionType": "semver",
              "lessThanOrEqual": "6.12.*"
            },
            {
              "status": "unaffected",
              "version": "6.18.50",
              "versionType": "semver",
              "lessThanOrEqual": "6.18.*"
            },
            {
              "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_wrap.c"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2026-09-11T20:19:37.380",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/075d7cfc4df8c54cb202ba8b28420370c03ba9b6",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/299d281c7225ded15b28cb861a98d818d82787fc",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/6959297aaa9572783d620a226d73c3fb94494888",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/806584a4b67a7233870c33e5b8f872e76dd02988",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/84ddbc8d084c0251d534f14f5d1a7da05be56404",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/dddcb0f4b7e27fac16a78ea9a1c8ec2e8a241087",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/f2591660e0eb263c9415bf0d0bb1b111e62df7a4",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Received",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nSUNRPC: harden gss_krb5_unwrap_v2 against short tokens\n\ngss_krb5_unwrap_v2() reads the EC and RRC header fields at ptr+4 and\nptr+6 before validating that the token is at least GSS_KRB5_TOK_HDR_LEN\n(16) bytes long, and its rotate_left() helper passes buf->len - base\nto xdr_buf_subsegment() without verifying that base <= buf->len. When\na caller hands in a sub-16-byte token, or a token whose declared len\nleaves base past the end of the buffer, three distinct failures follow:\n\n    gss_krb5_unwrap_v2(offset, len, buf)\n      ptr = buf->head[0].iov_base + offset\n      ec  = *(ptr + 4)              /* OOB read on short head */\n      rrc = *(ptr + 6)              /* OOB read on short head */\n      rotate_left(offset + 16, buf, rrc)\n        xdr_buf_subsegment(buf, &subbuf,\n                           base, buf->len - base)   /* u32 wrap when base > len */\n        _rotate_left(&subbuf, shift)\n          shift %= buf->len         /* divide-by-zero when base == len */\n\nAfter decryption, the cleanup arithmetic has the same shape:\n\n    movelen = min_t(unsigned int, buf->head[0].iov_len, len);\n    movelen -= offset + GSS_KRB5_TOK_HDR_LEN + headskip;\n    BUG_ON(offset + GSS_KRB5_TOK_HDR_LEN + headskip + movelen >\n                                            buf->head[0].iov_len);\n\nThe BUG_ON re-adds the value just subtracted, so it reduces to\nmin(A, B) > A and is permanently false; it cannot catch the unsigned\nunderflow of movelen, which then drives a ~UINT_MAX-byte memmove().\n\nAdd four defense-in-depth guards inside the unwrap core so it is safe\nregardless of what its callers validate:\n\n  - reject tokens with len - offset < GSS_KRB5_TOK_HDR_LEN before\n    touching ptr+4/ptr+6;\n  - bail from rotate_left() when buf->len <= base, covering both the\n    underflow and zero-length cases;\n  - return early from _rotate_left() when buf->len is zero, so the\n    shift %= buf->len modulo cannot fault;\n  - replace the dead BUG_ON with a live check that returns\n    GSS_S_DEFECTIVE_TOKEN before the movelen subtraction."
    }
  ],
  "lastModified": "2026-09-14T13:19:09.370",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}