CVE-2026-64456

Estado: RecibidaAlta (7.7)—

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

hwrng: virtio: clamp device-reported used.len at copy_data()

random_recv_done() stores the device-reported used.len directly into vi->data_avail. copy_data() then indexes vi->data[] using vi->data_idx (advanced by previous copy_data() calls) and issues a memcpy() without re-validating either value against the posted buffer size sizeof(vi->data) (SMP_CACHE_BYTES bytes, typically 32 or 64).

A malicious or buggy virtio-rng backend can set used.len beyond sizeof(vi->data), steering the memcpy() past the end of the inline array into adjacent kmalloc-1k slab bytes. hwrng_fillfn() mixes those bytes into the guest RNG, and guest root can also observe them directly via /dev/hwrng.

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Concrete impact is inside the guest:

Same class of bug as commit c04db81cd028 ("net/9p: Fix buffer overflow in USB transport layer"), which hardened usb9pfs_rx_complete() against unchecked device-reported length in the USB 9p transport.

With the clamp at point of use and array_index_nospec() in place, the same harness boots cleanly: copy_data() returns zero for the bogus report, the device-supplied bytes after data_idx are discarded, and the driver issues a fresh request.

Detalles técnicos trazas, registros y código del informe original

 - Memory-safety / hardening: any virtio-rng backend that
   over-reports used.len causes the driver to read past vi->data
   into unrelated slab contents.  hwrng_fillfn() is a kernel thread
   that runs as soon as the device is probed; no guest userspace
   interaction is required to first-trigger the OOB.

 - Cross-boundary leak (confidential-compute threat model): a
   malicious hypervisor cooperating with a malicious or compromised
   guest root userspace can use /dev/hwrng as a leak channel for
   guest-kernel heap data.  The host sets a large used.len, guest
   root reads /dev/hwrng, and the returned bytes contain guest
   kernel slab contents that were adjacent to vi->data.  In
   practice, confidential-compute guests (SEV-SNP, TDX) usually
   disable virtio-rng entirely, so this path is narrow, but the
   fix is still worth carrying because the underlying
   memory-safety bug contaminates the guest RNG on any host.

KASAN confirms the OOB on a 7.1-rc4 guest whose virtio-rng backend
has been patched to report used.len = 0x10000:

  BUG: KASAN: slab-out-of-bounds in virtio_read+0x394/0x5d0
  Read of size 64 at addr ffff88800ae0ba20 by task hwrng/52
  Call Trace:
   __asan_memcpy+0x23/0x60
   virtio_read+0x394/0x5d0
   hwrng_fillfn+0xb2/0x470
   kthread+0x2cc/0x3a0
  Allocated by task 1:
   probe_common+0xa5/0x660
   virtio_dev_probe+0x549/0xbc0
  The buggy address belongs to the object at ffff88800ae0b800
   which belongs to the cache kmalloc-1k of size 1024
  The buggy address is located 0 bytes to the right of
   allocated 544-byte region [ffff88800ae0b800, ffff88800ae0ba20)

CVSS

Versión: 3.1
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Puntuación base: 7.7

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.19%
Percentil entre todas las CVEs puntuadas: 8
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.

ExplotaciónT1068 Exploitation for Privilege Escalationprivilege escalation75 %
Impacto principalT1005 Data from Local Systemcollection80 %
Impacto secundarioT1499.004 Application or System Exploitationimpact65 %

Acceso local sin interacción (AV:L/PR:N/UI:N) en kernel Linux. Impacto: lectura OOB de datos kernel (T1005) y DoS por corrupción RNG (T1499.004).

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

Threat Intelligence Program Filter Network Traffic Execution Prevention Application Isolation and Sandboxing Exploit Protection Update Software

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-2026-64456",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 7.7,
          "attackVector": "LOCAL",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:L/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": 2.5
      }
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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          "vendor": "Linux",
          "product": "Linux",
          "versions": [
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              "versionType": "git"
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            {
              "status": "affected",
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              "versionType": "git"
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            {
              "status": "affected",
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          "programFiles": [
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        },
        {
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              "version": "2.6.26"
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              "version": "5.15.212",
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            },
            {
              "status": "unaffected",
              "version": "6.1.178",
              "versionType": "semver",
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            },
            {
              "status": "unaffected",
              "version": "6.6.145",
              "versionType": "semver",
              "lessThanOrEqual": "6.6.*"
            },
            {
              "status": "unaffected",
              "version": "6.12.96",
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              "lessThanOrEqual": "6.12.*"
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            {
              "status": "unaffected",
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            {
              "status": "unaffected",
              "version": "7.1.4",
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            },
            {
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "drivers/char/hw_random/virtio-rng.c"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2026-07-25T10:17:30.677",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/285e17c44e3873a73460f294acbd64018ff64385",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/fde19b0d4eeabae042519313c843fe6f27d41e9d",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Received",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nhwrng: virtio: clamp device-reported used.len at copy_data()\n\nrandom_recv_done() stores the device-reported used.len directly into\nvi->data_avail.  copy_data() then indexes vi->data[] using\nvi->data_idx (advanced by previous copy_data() calls) and issues a\nmemcpy() without re-validating either value against the posted\nbuffer size sizeof(vi->data) (SMP_CACHE_BYTES bytes, typically 32\nor 64).\n\nA malicious or buggy virtio-rng backend can set used.len beyond\nsizeof(vi->data), steering the memcpy() past the end of the inline\narray into adjacent kmalloc-1k slab bytes.  hwrng_fillfn() mixes\nthose bytes into the guest RNG, and guest root can also observe\nthem directly via /dev/hwrng.\n\nConcrete impact is inside the guest:\n\n - Memory-safety / hardening: any virtio-rng backend that\n   over-reports used.len causes the driver to read past vi->data\n   into unrelated slab contents.  hwrng_fillfn() is a kernel thread\n   that runs as soon as the device is probed; no guest userspace\n   interaction is required to first-trigger the OOB.\n\n - Cross-boundary leak (confidential-compute threat model): a\n   malicious hypervisor cooperating with a malicious or compromised\n   guest root userspace can use /dev/hwrng as a leak channel for\n   guest-kernel heap data.  The host sets a large used.len, guest\n   root reads /dev/hwrng, and the returned bytes contain guest\n   kernel slab contents that were adjacent to vi->data.  In\n   practice, confidential-compute guests (SEV-SNP, TDX) usually\n   disable virtio-rng entirely, so this path is narrow, but the\n   fix is still worth carrying because the underlying\n   memory-safety bug contaminates the guest RNG on any host.\n\nKASAN confirms the OOB on a 7.1-rc4 guest whose virtio-rng backend\nhas been patched to report used.len = 0x10000:\n\n  BUG: KASAN: slab-out-of-bounds in virtio_read+0x394/0x5d0\n  Read of size 64 at addr ffff88800ae0ba20 by task hwrng/52\n  Call Trace:\n   __asan_memcpy+0x23/0x60\n   virtio_read+0x394/0x5d0\n   hwrng_fillfn+0xb2/0x470\n   kthread+0x2cc/0x3a0\n  Allocated by task 1:\n   probe_common+0xa5/0x660\n   virtio_dev_probe+0x549/0xbc0\n  The buggy address belongs to the object at ffff88800ae0b800\n   which belongs to the cache kmalloc-1k of size 1024\n  The buggy address is located 0 bytes to the right of\n   allocated 544-byte region [ffff88800ae0b800, ffff88800ae0ba20)\n\nSame class of bug as commit c04db81cd028 (\"net/9p: Fix buffer\noverflow in USB transport layer\"), which hardened\nusb9pfs_rx_complete() against unchecked device-reported length in\nthe USB 9p transport.\n\nWith the clamp at point of use and array_index_nospec() in place,\nthe same harness boots cleanly: copy_data() returns zero for the\nbogus report, the device-supplied bytes after data_idx are\ndiscarded, and the driver issues a fresh request."
    }
  ],
  "lastModified": "2026-08-17T05:17:50.710",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}