Skip to content
Fencer Vulns
high 7.8

CVE-2025-39823 json

KVM: x86: use array_index_nospec with indices that come from guest

published 2025-09-16 13 mo ago modified 2026-11-05 3 d ago also EUVD-2025-29591

cvss
7.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 7%
public exploits
0
none known

Summary

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

KVM: x86: use array_index_nospec with indices that come from guest

min and dest_id are guest-controlled indices. Using array_index_nospec() after the bounds checks clamps these values to mitigate speculative execution side-channels.

Patch / fix

  • Linux Linux 5.4.298, 5.10.242, 5.15.191, 6.1.150, 6.6.104, 6.12.45, 6.16.5, 6.17
  • Siemens SIMATIC CN 4100 V5.0
  • linux Debian 12 6.1.153-1
  • linux Debian 13 6.12.48-1
  • linux Debian 14 6.16.5-1

debian advisories DEBIAN-CVE-2025-39823

  • linux Ubuntu 22.04 LTS 5.15.0-163.173
  • linux Ubuntu 24.04 LTS 6.8.0-106.106
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1097.104
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1050.53
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1097.106
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1052.55
  • linux-gke Ubuntu 22.04 LTS 5.15.0-1093.99
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1048.53

ubuntu advisories UBUNTU-CVE-2025-39823

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-rt Linux Micro 6.2 6.12.0-160000.6.1
  • kernel-64kb SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.6.1
  • kernel-source SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.6.1
  • kernel-default SLES 16.0, SLE High Availability Extension 16.0, Linux Micro 6.2 +1 more 6.12.0-160000.6.1
  • kernel-default-base SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.6.1.160000.2.4
  • kernel-syms SLES 16.0, Linux Micro Extras 6.2, SLES for SAP applications 16.0 6.12.0-160000.6.1
  • kernel-obs-qa SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.6.1
  • kernel-kvmsmall SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.6.1

suse advisories SUSE-SU-2025:21074-1SUSE-SU-2025:21139-1SUSE-SU-2026:20560-1SUSE-SU-2025:21179-1SUSE-SU-2025:20870-1SUSE-SU-2025:3761-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.6.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-kvmsmall openSUSE Leap 16.0 6.12.0-160000.6.1

opensuse advisories openSUSE-SU-2025:20081-1

  • kernel Azure Linux 3.0 6.6.104.2-1
  • kernel CBL-Mariner 2.0 5.15.200.1-1

azure linux advisories AZL-67419AZL-74718

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-2025-39823 updated cvss 5.1

kernel: KVM: x86: use array_index_nospec with indices that come from guest

  • 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 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux 10 kernel
    affected: no fix available “Fix deferred”
  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 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
3 d ago

Exploit prediction

0.18% chance of exploitation in the next 30 days, higher than 7% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Linux Linux
  • Siemens SIMATIC CN 4100

Classification

Weakness
  • CWE-129 Improper Validation of Array Index
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.