CVE-2026-64456

Status: UPDATED  |  Advisory ID: CVE-2026-64456

Key Details

Affected Products, Subsystems & Sectors

What to Know

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. (NVD)

What to Do

Monitor Linux's web page for any future patch releases.

References