CVE-2026-74751

Estado: RecibidaCrítica (9.4)—

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

riscv: lib: Fix ZBB strnlen reading past count boundary

The ZBB-optimized strnlen loop loads one word ahead before checking the aligned boundary:

where t4 = (s + count) & -SZREG. When s is aligned and count is a multiple of SZREG, t4 equals s + count and the loop loads a full word starting at exactly s + count. If s + count falls on a page boundary with the next page unmapped, this faults.

Fix by computing the aligned boundary from the last valid byte (s + count - 1) instead of s + count. This makes the loop stop at the word containing the last valid byte rather than potentially loading the word after it. The count == 0 case is already handled by the beqz early exit.

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Also add a pre-loop guard (bgeu t0, t4) for the case where all valid bytes fit within the first word. With the adjusted boundary, t4 can equal t0, and entering the loop with stale register state from the first-word processing would produce incorrect results.

The final minu clamp ensures the result is still correct when the last loaded word extends past s + count - 1 within the same aligned word.

Detalles técnicos trazas, registros y código del informe original

    REG_L   t1, SZREG(t0)       // load next word
    addi    t0, t0, SZREG       // advance
    orc.b   t1, t1
    bgeu    t0, t4, 4f          // boundary check AFTER load

CVSS

Versión: 3.1
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:H
Puntuación base: 9.4

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.46%
Percentil entre todas las CVEs puntuadas: 38
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 access60 %

Inferido por reglas deterministas a partir del vector CVSS y la CWE. Solo orientativo.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Vulnerability Scanning Privileged Account Management Network Segmentation Limit Access to Resource Over Network Filter Network Traffic 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)

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{
  "id": "CVE-2026-74751",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 9.4,
          "attackVector": "NETWORK",
          "baseSeverity": "CRITICAL",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:H",
          "integrityImpact": "LOW",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.5,
        "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": "5ba15d419fab848a3813eb56bbcad00e291fbc49",
              "lessThan": "e697e30f3dd2da3a1df7dc0980546d5b53aea4b6",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "5ba15d419fab848a3813eb56bbcad00e291fbc49",
              "lessThan": "5d588c684833e678a0008eb69c33190f01a65f4b",
              "versionType": "git"
            }
          ],
          "programFiles": [
            "arch/riscv/lib/strnlen.S"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "7.1"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "7.1",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "7.1.10",
              "versionType": "semver",
              "lessThanOrEqual": "7.1.*"
            },
            {
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "arch/riscv/lib/strnlen.S"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2026-08-26T15:16:54.160",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/5d588c684833e678a0008eb69c33190f01a65f4b",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/e697e30f3dd2da3a1df7dc0980546d5b53aea4b6",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Received",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nriscv: lib: Fix ZBB strnlen reading past count boundary\n\nThe ZBB-optimized strnlen loop loads one word ahead before checking the\naligned boundary:\n\n    REG_L   t1, SZREG(t0)       // load next word\n    addi    t0, t0, SZREG       // advance\n    orc.b   t1, t1\n    bgeu    t0, t4, 4f          // boundary check AFTER load\n\nwhere t4 = (s + count) & -SZREG.  When s is aligned and count is a\nmultiple of SZREG, t4 equals s + count and the loop loads a full word\nstarting at exactly s + count.  If s + count falls on a page boundary\nwith the next page unmapped, this faults.\n\nFix by computing the aligned boundary from the last valid byte\n(s + count - 1) instead of s + count.  This makes the loop stop at the\nword containing the last valid byte rather than potentially loading the\nword after it.  The count == 0 case is already handled by the beqz\nearly exit.\n\nAlso add a pre-loop guard (bgeu t0, t4) for the case where all valid\nbytes fit within the first word.  With the adjusted boundary, t4 can\nequal t0, and entering the loop with stale register state from the\nfirst-word processing would produce incorrect results.\n\nThe final minu clamp ensures the result is still correct when the last\nloaded word extends past s + count - 1 within the same aligned word."
    }
  ],
  "lastModified": "2026-08-27T06:17:26.247",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}