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Fencer Vulns
high 7.7

CVE-2026-64456 json

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

published 2026-07-25 3 mo ago modified 2026-11-03 5 d ago also EUVD-2026-48800

cvss
7.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.1%
EPSS 0.1% chance of exploitation in 30 days, percentile 4%
public exploits
0
none known

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.

Patch / fix

  • Linux Linux 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.96, 6.18.39, 7.1.4, 7.2
  • linux Debian 12 6.1.180-1
  • linux Debian 13 6.12.96-1
  • linux Debian 14 7.1.4-1
  • linux-6.12 Debian 12 6.12.100-1~deb12u1

debian advisories DEBIAN-CVE-2026-64456

  • linux Ubuntu 22.04 LTS 5.15.0-198.208
  • linux Ubuntu 24.04 LTS 6.8.0-147.147
  • linux Ubuntu 26.04 LTS 7.0.0-31.31
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1117.124
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1067.70
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1012.12
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1118.128
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1071.79

ubuntu advisories UBUNTU-CVE-2026-64456

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel RHEL 10.2 6.12.0-211.56.1.el10_2
  • rv RHEL 10.2 6.12.0-211.56.1.el10_2
  • perf RHEL 10.2 6.12.0-211.56.1.el10_2
  • rtla RHEL 10.2 6.12.0-211.56.1.el10_2
  • libperf RHEL 10.2 6.12.0-211.56.1.el10_2
  • kernel-rt RHEL 10.2 6.12.0-211.56.1.el10_2
  • kernel-64k RHEL 10.2 6.12.0-211.56.1.el10_2
  • kernel-core RHEL 10.2 6.12.0-211.56.1.el10_2

red hat advisories RHSA-2026:68507

  • kernel-rt Linux Micro 6.2 6.12.0-160000.38.1
  • kernel-64kb SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.38.1
  • kernel-source SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.38.1
  • kernel-default SLES 16.0, SLE High Availability Extension 16.0, Linux Micro 6.2 +1 more 6.12.0-160000.38.1
  • kernel-default-base SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.38.1.160000.2.23
  • kernel-syms SLES 16.0, Linux Micro Extras 6.2, SLES for SAP applications 16.0 6.12.0-160000.38.1
  • kernel-azure SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.38.1
  • kernel-obs-qa SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.38.1

suse advisories SUSE-SU-2026:4892-1SUSE-SU-2026:23887-1SUSE-SU-2026:23902-1SUSE-SU-2026:23897-1SUSE-SU-2026:23881-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.38.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.38.1

opensuse advisories openSUSE-SU-2026:21910-1openSUSE-SU-2026:11476-1

  • kernel AlmaLinux 10 6.12.0-211.56.1.el10_2
  • rv AlmaLinux 10 6.12.0-211.56.1.el10_2
  • perf AlmaLinux 10 6.12.0-211.56.1.el10_2
  • rtla AlmaLinux 10 6.12.0-211.56.1.el10_2
  • libperf AlmaLinux 10 6.12.0-211.56.1.el10_2
  • kernel-rt AlmaLinux 10 6.12.0-211.56.1.el10_2
  • kernel-64k AlmaLinux 10 6.12.0-211.56.1.el10_2
  • kernel-core AlmaLinux 10 6.12.0-211.56.1.el10_2

almalinux advisories ALSA-2026:68507

  • kernel Rocky Linux 10 6.12.0-211.56.1.el10_2.0.1

rocky linux advisories RLSA-2026:68507

  • kernel Azure Linux 3.0 6.6.145.2-1

azure linux advisories AZL-93866

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-64456 updated cvss 7.0

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

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 kernel-rt, kernel-rt-kvm, kernel-rt-trace, kernel-rt-debug-kvm, kernel-rt-trace-kvm Red Hat Enterprise Linux 8 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +6 more Red Hat Enterprise Linux 9 kernel-rt, kernel-rt-selftests-internal
    affected: no fix available
  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-211.56.1.el10_2, perf 6.12.0-211.56.1.el10_2, rtla 6.12.0-211.56.1.el10_2, python3-perf 6.12.0-211.56.1.el10_2, kernel-devel-matched 6.12.0-211.56.1.el10_2, kernel-64k-devel-matched 6.12.0-211.56.1.el10_2, +7 more Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-211.56.1.el10_2, kernel-64k 6.12.0-211.56.1.el10_2, kernel-core 6.12.0-211.56.1.el10_2, kernel-tools 6.12.0-211.56.1.el10_2, kernel-modules 6.12.0-211.56.1.el10_2, kernel-64k-core 6.12.0-211.56.1.el10_2, +28 more Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-211.56.1.el10_2, kernel-debuginfo-common-s390x 6.12.0-211.56.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.56.1.el10_2, kernel-debuginfo-common-aarch64 6.12.0-211.56.1.el10_2, kernel-debuginfo-common-ppc64le 6.12.0-211.56.1.el10_2 Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-211.56.1.el10_2, kernel-rt-64k 6.12.0-211.56.1.el10_2, kernel-rt-core 6.12.0-211.56.1.el10_2, kernel-rt-modules 6.12.0-211.56.1.el10_2, kernel-rt-64k-core 6.12.0-211.56.1.el10_2, kernel-rt-debug-core 6.12.0-211.56.1.el10_2, +14 more Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-211.56.1.el10_2, kernel-rt-core 6.12.0-211.56.1.el10_2, kernel-rt-modules 6.12.0-211.56.1.el10_2, kernel-rt-debug-core 6.12.0-211.56.1.el10_2, kernel-rt-modules-core 6.12.0-211.56.1.el10_2, kernel-rt-debug-modules 6.12.0-211.56.1.el10_2, +4 more
    fixed: vendor fix RHSA-2026:68507
  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, python-perf, kernel-kdump, kernel-tools, +3 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-core, kernel-tools, python3-perf, +17 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +82 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
23 d ago

Exploit prediction

0.15% chance of exploitation in the next 30 days, higher than 4% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.7 CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

Affected products

  • Linux Linux

Classification

Weakness
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.