CVE-2026-64456 (GCVE-0-2026-64456)

Vulnerability from cvelistv5 – Published: 2026-07-25 08:51 – Updated: 2026-08-17 04:56
VLAI
Title
hwrng: virtio: clamp device-reported used.len at copy_data()
Summary
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. Concrete impact is inside the guest: - 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) 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.
Severity
7.7 (High)
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: f7f510ec195781c857ab76366a3e1c59e1caae42 , < 3aa3e89cf80721c8d382b4c1a2b70a0449dad4a5 (git)
Affected: f7f510ec195781c857ab76366a3e1c59e1caae42 , < 63335e7b638ae70028ae285bb95153874a8bc852 (git)
Affected: f7f510ec195781c857ab76366a3e1c59e1caae42 , < 2e788948ff2a13358a303af112497a63201c5739 (git)
Affected: f7f510ec195781c857ab76366a3e1c59e1caae42 , < fde19b0d4eeabae042519313c843fe6f27d41e9d (git)
Affected: f7f510ec195781c857ab76366a3e1c59e1caae42 , < 81dd21b5f0c299cc7b5bf84f04a61938559d20e6 (git)
Affected: f7f510ec195781c857ab76366a3e1c59e1caae42 , < 285e17c44e3873a73460f294acbd64018ff64385 (git)
Affected: f7f510ec195781c857ab76366a3e1c59e1caae42 , < 92d5736a62040ec1cfff23ea57e6599301690ad5 (git)
Affected: f7f510ec195781c857ab76366a3e1c59e1caae42 , < e3046eeada299f917a8ad883af4434bfb86556b1 (git)
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Linux Linux Affected: 2.6.26
Unaffected: 0 , < 2.6.26 (semver)
Unaffected: 5.10.261 , ≤ 5.10.* (semver)
Unaffected: 5.15.212 , ≤ 5.15.* (semver)
Unaffected: 6.1.178 , ≤ 6.1.* (semver)
Unaffected: 6.6.145 , ≤ 6.6.* (semver)
Unaffected: 6.12.96 , ≤ 6.12.* (semver)
Unaffected: 6.18.39 , ≤ 6.18.* (semver)
Unaffected: 7.1.4 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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{
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      "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-\u003edata_avail.  copy_data() then indexes vi-\u003edata[] using\nvi-\u003edata_idx (advanced by previous copy_data() calls) and issues a\nmemcpy() without re-validating either value against the posted\nbuffer size sizeof(vi-\u003edata) (SMP_CACHE_BYTES bytes, typically 32\nor 64).\n\nA malicious or buggy virtio-rng backend can set used.len beyond\nsizeof(vi-\u003edata), 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-\u003edata\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-\u003edata.  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."
        }
      ],
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        {
          "cvssV3_1": {
            "baseScore": 7.7,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H",
            "version": "3.1"
          },
          "scenarios": [
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              "value": "AV:L - The attacker must control a virtio-rng backend or hypervisor locally attached to the guest; no network or physical packet path reaches this driver.\nAC:L - The backend directly controls the 32-bit used.len and can deterministically over-report it without winning a race or manipulating an uncertain memory layout.\nPR:N - No privileges inside the vulnerable guest are required because the hwrng kernel thread automatically consumes backend completions after device registration.\nUI:N - The automatically started hwrng thread triggers the out-of-bounds read without any victim action or guest userspace request.\nS:U - The vulnerable driver and the affected memory, RNG state, and availability all belong to the same guest-kernel security authority; this is not a guest-to-host escape.\nC:H - Repeated bounded copies advance through a device-selected, potentially enormous length, producing sequential out-of-bounds reads of guest-kernel heap memory that guest root can observe through /dev/hwrng.\nI:N - The memcpy destination remains bounded by the hwrng core buffer, so the flaw provides no out-of-bounds write, use-after-free, or control-flow modification primitive.\nA:H - A sufficiently large reported length drives reads beyond valid slab memory, causing a kernel out-of-bounds fault, oops, or panic, and the malicious backend can trigger it repeatedly."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T04:56:00.610Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/3aa3e89cf80721c8d382b4c1a2b70a0449dad4a5"
        },
        {
          "url": "https://git.kernel.org/stable/c/63335e7b638ae70028ae285bb95153874a8bc852"
        },
        {
          "url": "https://git.kernel.org/stable/c/2e788948ff2a13358a303af112497a63201c5739"
        },
        {
          "url": "https://git.kernel.org/stable/c/fde19b0d4eeabae042519313c843fe6f27d41e9d"
        },
        {
          "url": "https://git.kernel.org/stable/c/81dd21b5f0c299cc7b5bf84f04a61938559d20e6"
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        {
          "url": "https://git.kernel.org/stable/c/e3046eeada299f917a8ad883af4434bfb86556b1"
        }
      ],
      "title": "hwrng: virtio: clamp device-reported used.len at copy_data()",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64456",
    "datePublished": "2026-07-25T08:51:24.659Z",
    "dateReserved": "2026-07-19T15:36:31.789Z",
    "dateUpdated": "2026-08-17T04:56:00.610Z",
    "state": "PUBLISHED"
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    "epss": {
      "cve": "CVE-2026-64456",
      "date": "2026-09-21",
      "epss": "0.00148",
      "percentile": "0.04389"
    },
    "microsoft_vex": {
      "current_release_date": "2026-07-27T14:40:39.000Z",
      "cve": "CVE-2026-64456",
      "id": "msrc_CVE-2026-64456",
      "initial_release_date": "2026-07-26T01:10:12.000Z",
      "product_status:known_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "hwrng: virtio: clamp device-reported used.len at copy_data()",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-64456.json",
      "version": "2"
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          {
            "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-\u003edata_avail.  copy_data() then indexes vi-\u003edata[] using\nvi-\u003edata_idx (advanced by previous copy_data() calls) and issues a\nmemcpy() without re-validating either value against the posted\nbuffer size sizeof(vi-\u003edata) (SMP_CACHE_BYTES bytes, typically 32\nor 64).\n\nA malicious or buggy virtio-rng backend can set used.len beyond\nsizeof(vi-\u003edata), 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-\u003edata\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-\u003edata.  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."
          }
        ],
        "id": "CVE-2026-64456",
        "lastModified": "2026-08-17T05:17:50.710",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "LOCAL",
                "availabilityImpact": "HIGH",
                "baseScore": 7.7,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "NONE",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H",
                "version": "3.1"
              },
              "exploitabilityScore": 2.5,
              "impactScore": 5.2,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
            }
          ]
        },
        "published": "2026-07-25T10:17:30.677",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/285e17c44e3873a73460f294acbd64018ff64385"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/2e788948ff2a13358a303af112497a63201c5739"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/3aa3e89cf80721c8d382b4c1a2b70a0449dad4a5"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/63335e7b638ae70028ae285bb95153874a8bc852"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/81dd21b5f0c299cc7b5bf84f04a61938559d20e6"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/92d5736a62040ec1cfff23ea57e6599301690ad5"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/e3046eeada299f917a8ad883af4434bfb86556b1"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/fde19b0d4eeabae042519313c843fe6f27d41e9d"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-09-17T12:42:31+00:00",
      "cve": "CVE-2026-64456",
      "id": "CVE-2026-64456",
      "initial_release_date": "2026-07-25T00:00:00+00:00",
      "product_status:fixed": "309",
      "product_status:known_affected": "43",
      "product_status:known_not_affected": "156",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: hwrng: virtio: clamp device-reported used.len at copy_data()",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-64456.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-19T01:51:41Z",
      "cve": "CVE-2026-64456",
      "id": "CVE-2026-64456",
      "initial_release_date": "2026-07-25T15:58:58Z",
      "product_status:known_affected": "281",
      "product_status:known_not_affected": "95",
      "product_status:recommended": "46",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-64456",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-64456.json",
      "version": "7"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.


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Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.