CVE-2026-64456 (GCVE-0-2026-64456)
Vulnerability from cvelistv5
Published
2026-07-25 08:51
Modified
2026-08-17 04:56
Severity ?
VLAI Severity ?
EPSS score ?
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.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: f7f510ec195781c857ab76366a3e1c59e1caae42 Version: f7f510ec195781c857ab76366a3e1c59e1caae42 Version: f7f510ec195781c857ab76366a3e1c59e1caae42 Version: f7f510ec195781c857ab76366a3e1c59e1caae42 Version: f7f510ec195781c857ab76366a3e1c59e1caae42 Version: f7f510ec195781c857ab76366a3e1c59e1caae42 Version: f7f510ec195781c857ab76366a3e1c59e1caae42 Version: f7f510ec195781c857ab76366a3e1c59e1caae42 |
||
{
"containers": {
"cna": {
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"programFiles": [
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],
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],
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"vendor": "Linux",
"versions": [
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"version": "0",
"versionType": "semver"
},
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},
{
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"status": "unaffected",
"version": "5.15.212",
"versionType": "semver"
},
{
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"status": "unaffected",
"version": "6.1.178",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"version": "6.6.145",
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},
{
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"version": "6.12.96",
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},
{
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"status": "unaffected",
"version": "6.18.39",
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},
{
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"status": "unaffected",
"version": "7.1.4",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.2",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
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"negate": false,
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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."
}
],
"metrics": [
{
"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": [
{
"lang": "en",
"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"
},
{
"url": "https://git.kernel.org/stable/c/285e17c44e3873a73460f294acbd64018ff64385"
},
{
"url": "https://git.kernel.org/stable/c/92d5736a62040ec1cfff23ea57e6599301690ad5"
},
{
"url": "https://git.kernel.org/stable/c/e3046eeada299f917a8ad883af4434bfb86556b1"
}
],
"title": "hwrng: virtio: clamp device-reported used.len at copy_data()",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"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"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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