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Fencer Vulns
high 7.8

CVE-2025-21991 json

x86/microcode/AMD: Fix out-of-bounds on systems with CPU-less NUMA nodes

published 2025-04-02 19 mo ago modified 2026-06-17 4 mo ago also EUVD-2025-9538

cvss
7.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 13%
public exploits
0
none known

Summary

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

x86/microcode/AMD: Fix out-of-bounds on systems with CPU-less NUMA nodes

Currently, load_microcode_amd() iterates over all NUMA nodes, retrieves their CPU masks and unconditionally accesses per-CPU data for the first CPU of each mask.

According to Documentation/admin-guide/mm/numaperf.rst:

"Some memory may share the same node as a CPU, and others are provided as memory only nodes."

Therefore, some node CPU masks may be empty and wouldn't have a "first CPU".

On a machine with far memory (and therefore CPU-less NUMA nodes): - cpumask_of_node(nid) is 0 - cpumask_first(0) is CONFIG_NR_CPUS - cpu_data(CONFIG_NR_CPUS) accesses the cpu_info per-CPU array at an index that is 1 out of bounds

This does not have any security implications since flashing microcode is a privileged operation but I believe this has reliability implications by potentially corrupting memory while flashing a microcode update.

When booting with CONFIG_UBSAN_BOUNDS=y on an AMD machine that flashes a microcode update. I get the following splat:

UBSAN: array-index-out-of-bounds in arch/x86/kernel/cpu/microcode/amd.c:X:Y index 512 is out of range for type 'unsigned long[512]' [...] Call Trace: dump_stack __ubsan_handle_out_of_bounds load_microcode_amd request_microcode_amd reload_store kernfs_fop_write_iter vfs_write ksys_write do_syscall_64 entry_SYSCALL_64_after_hwframe

Change the loop to go over only NUMA nodes which have CPUs before determining whether the first CPU on the respective node needs microcode update.

[ bp: Massage commit message, fix typo. ]

Patch / fix

  • Linux Linux 4.15, 4.20, 5.4.292, 5.10.236, 5.15.180, 6.1.132, 6.3, 6.6.84, 6.12.20, 6.13.8, 6.14
  • linux Debian 12 6.1.133-1
  • linux Debian 14, Debian 13 6.12.20-1

debian advisories DEBIAN-CVE-2025-21991

  • linux Ubuntu 22.04 LTS 5.15.0-142.152
  • linux Ubuntu 24.04 LTS 6.8.0-84.84
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1086.93
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1039.41
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1085.94
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1040.42
  • linux-gke Ubuntu 22.04 LTS 5.15.0-1083.89
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1036.40

ubuntu advisories UBUNTU-CVE-2025-21991

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 8 4.18.0-553.62.1.el8_10
  • perf RHEL 8 4.18.0-553.62.1.el8_10
  • bpftool RHEL 8 4.18.0-553.62.1.el8_10
  • kernel-core RHEL 8 4.18.0-553.62.1.el8_10
  • kernel-tools RHEL 8 4.18.0-553.62.1.el8_10
  • python3-perf RHEL 8 4.18.0-553.62.1.el8_10
  • kernel-modules RHEL 8 4.18.0-553.62.1.el8_10
  • kernel-zfcpdump RHEL 8 4.18.0-553.62.1.el8_10

red hat advisories RHSA-2025:14094RHSA-2025:14054RHSA-2025:13781RHSA-2025:13633RHSA-2025:13135RHSA-2025:11298

  • kernel-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.20.3.1
  • kernel-syms-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.20.3.1
  • kernel-source-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.20.3.1
  • kernel-rt Real Time Module 15 SP6, openSUSE Leap 15.6 6.4.0-150600.10.39.1
  • kernel-syms-rt Real Time Module 15 SP6, openSUSE Leap 15.6 6.4.0-150600.10.39.1
  • kernel-rt_debug Real Time Module 15 SP6, openSUSE Leap 15.6 6.4.0-150600.10.39.1
  • kernel-source-rt Real Time Module 15 SP6, openSUSE Leap 15.6 6.4.0-150600.10.39.1
  • kernel-64kb SLE Module for Basesystem 15 SP7 6.4.0-150700.53.3.1

suse advisories SUSE-SU-2025:01967-1SUSE-SU-2025:01964-1SUSE-SU-2025:01951-1SUSE-SU-2025:01919-1SUSE-SU-2025:01707-1SUSE-SU-2025:01614-1

  • kernel AlmaLinux 8 4.18.0-553.62.1.el8_10
  • perf AlmaLinux 8 4.18.0-553.62.1.el8_10
  • bpftool AlmaLinux 8 4.18.0-553.62.1.el8_10
  • kernel-core AlmaLinux 8 4.18.0-553.62.1.el8_10
  • kernel-tools AlmaLinux 8 4.18.0-553.62.1.el8_10
  • python3-perf AlmaLinux 8 4.18.0-553.62.1.el8_10
  • kernel-modules AlmaLinux 8 4.18.0-553.62.1.el8_10
  • kernel-zfcpdump AlmaLinux 8 4.18.0-553.62.1.el8_10

almalinux advisories ALSA-2025:11298ALSA-2025:11299ALSA-2025:10837ALSA-2025:10371

  • kernel Rocky Linux 9 5.14.0-570.26.1.el9_6
  • kernel Rocky Linux 10 6.12.0-55.20.1.el10_0
  • kernel-rt Rocky Linux 8 4.18.0-553.62.1.rt7.403.el8_10
  • kernel Rocky Linux 8 4.18.0-553.62.1.el8_10

rocky linux advisories RLSA-2025:10837RLSA-2025:10371RLSA-2025:11299RLSA-2025:11298

  • kernel CBL-Mariner 2.0 5.15.180.1-1
  • kernel Azure Linux 3.0 6.6.85.1-2

azure linux advisories AZL-59785AZL-59843

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-2025-21991 updated cvss 6.7

kernel: x86/microcode/AMD: Fix out-of-bounds on systems with CPU-less NUMA nodes

  • Red Hat Enterprise Linux 9 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +12 more
    affected: no fix available
  • Red Hat CodeReady Linux Builder EUS (v.9.4) libperf 5.14.0-427.81.1.el9_4, kernel-debuginfo-common-s390x 5.14.0-427.81.1.el9_4, kernel-debuginfo-common-x86_64 5.14.0-427.81.1.el9_4, kernel-debuginfo-common-aarch64 5.14.0-427.81.1.el9_4, kernel-debuginfo-common-ppc64le 5.14.0-427.81.1.el9_4
    fixed: vendor fix RHSA-2025:13135
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-570.26.1.el9_6, perf 5.14.0-570.26.1.el9_6, rtla 5.14.0-570.26.1.el9_6, python3-perf 5.14.0-570.26.1.el9_6, kernel-devel-matched 5.14.0-570.26.1.el9_6, kernel-64k-devel-matched 5.14.0-570.26.1.el9_6, +7 more
    fixed: vendor fix RHSA-2025:10837
  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-55.20.1.el10_0, perf 6.12.0-55.20.1.el10_0, rtla 6.12.0-55.20.1.el10_0, python3-perf 6.12.0-55.20.1.el10_0, kernel-devel-matched 6.12.0-55.20.1.el10_0, kernel-64k-devel-matched 6.12.0-55.20.1.el10_0, +7 more
    fixed: vendor fix RHSA-2025:10371
  • Red Hat Enterprise Linux AppStream E4S (v.9.0) perf 5.14.0-70.142.1.el9_0, kernel-devel-matched 5.14.0-70.142.1.el9_0, kernel-debug-devel-matched 5.14.0-70.142.1.el9_0, kernel-debuginfo-common-s390x 5.14.0-70.142.1.el9_0, kernel-zfcpdump-devel-matched 5.14.0-70.142.1.el9_0, kernel-debuginfo-common-x86_64 5.14.0-70.142.1.el9_0, +2 more
    fixed: vendor fix RHSA-2025:14054
  • Red Hat Enterprise Linux AppStream E4S (v.9.2) perf 5.14.0-284.130.1.el9_2, rtla 5.14.0-284.130.1.el9_2, kernel-devel-matched 5.14.0-284.130.1.el9_2, kernel-64k-devel-matched 5.14.0-284.130.1.el9_2, kernel-debug-devel-matched 5.14.0-284.130.1.el9_2, kernel-debuginfo-common-s390x 5.14.0-284.130.1.el9_2, +5 more
    fixed: vendor fix RHSA-2025:13781
  • Red Hat Enterprise Linux AppStream EUS (v.9.4) rv 5.14.0-427.81.1.el9_4, perf 5.14.0-427.81.1.el9_4, rtla 5.14.0-427.81.1.el9_4, kernel-devel-matched 5.14.0-427.81.1.el9_4, kernel-64k-devel-matched 5.14.0-427.81.1.el9_4, kernel-debug-devel-matched 5.14.0-427.81.1.el9_4, +6 more
    fixed: vendor fix RHSA-2025:13135
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-553.62.1.el8_10, kernel 4.18.0-553.62.1.el8_10, bpftool 4.18.0-553.62.1.el8_10, kernel-core 4.18.0-553.62.1.el8_10, kernel-tools 4.18.0-553.62.1.el8_10, python3-perf 4.18.0-553.62.1.el8_10, +15 more
    fixed: vendor fix RHSA-2025:11298
show 21 more
  • Red Hat Enterprise Linux BaseOS (v. 9) kernel 5.14.0-570.26.1.el9_6, kernel-64k 5.14.0-570.26.1.el9_6, kernel-core 5.14.0-570.26.1.el9_6, kernel-tools 5.14.0-570.26.1.el9_6, kernel-modules 5.14.0-570.26.1.el9_6, kernel-64k-core 5.14.0-570.26.1.el9_6, +27 more
    fixed: vendor fix RHSA-2025:10837
  • Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-55.20.1.el10_0, kernel-64k 6.12.0-55.20.1.el10_0, kernel-core 6.12.0-55.20.1.el10_0, kernel-tools 6.12.0-55.20.1.el10_0, kernel-modules 6.12.0-55.20.1.el10_0, kernel-64k-core 6.12.0-55.20.1.el10_0, +27 more
    fixed: vendor fix RHSA-2025:10371
  • Red Hat Enterprise Linux BaseOS E4S (v.9.0) kernel 5.14.0-70.142.1.el9_0, bpftool 5.14.0-70.142.1.el9_0, kernel-core 5.14.0-70.142.1.el9_0, kernel-tools 5.14.0-70.142.1.el9_0, python3-perf 5.14.0-70.142.1.el9_0, kernel-modules 5.14.0-70.142.1.el9_0, +14 more
    fixed: vendor fix RHSA-2025:14054
  • Red Hat Enterprise Linux BaseOS E4S (v.9.2) bpftool 7.0.0-284.130.1.el9_2, kernel 5.14.0-284.130.1.el9_2, kernel-64k 5.14.0-284.130.1.el9_2, kernel-core 5.14.0-284.130.1.el9_2, kernel-tools 5.14.0-284.130.1.el9_2, python3-perf 5.14.0-284.130.1.el9_2, +28 more
    fixed: vendor fix RHSA-2025:13781
  • Red Hat Enterprise Linux BaseOS EUS (v.9.4) bpftool 7.3.0-427.81.1.el9_4, kernel 5.14.0-427.81.1.el9_4, kernel-64k 5.14.0-427.81.1.el9_4, kernel-core 5.14.0-427.81.1.el9_4, kernel-tools 5.14.0-427.81.1.el9_4, python3-perf 5.14.0-427.81.1.el9_4, +28 more
    fixed: vendor fix RHSA-2025:13135
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) libperf 5.14.0-570.26.1.el9_6, kernel-debuginfo-common-s390x 5.14.0-570.26.1.el9_6, kernel-debuginfo-common-x86_64 5.14.0-570.26.1.el9_6, kernel-debuginfo-common-aarch64 5.14.0-570.26.1.el9_6, kernel-debuginfo-common-ppc64le 5.14.0-570.26.1.el9_6
    fixed: vendor fix RHSA-2025:10837
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-55.20.1.el10_0, kernel-debuginfo-common-s390x 6.12.0-55.20.1.el10_0, kernel-debuginfo-common-x86_64 6.12.0-55.20.1.el10_0, kernel-debuginfo-common-aarch64 6.12.0-55.20.1.el10_0, kernel-debuginfo-common-ppc64le 6.12.0-55.20.1.el10_0
    fixed: vendor fix RHSA-2025:10371
  • Red Hat Enterprise Linux CRB (v. 8) kernel-debuginfo-common-x86_64 4.18.0-553.62.1.el8_10, kernel-debuginfo-common-aarch64 4.18.0-553.62.1.el8_10, kernel-debuginfo-common-ppc64le 4.18.0-553.62.1.el8_10
    fixed: vendor fix RHSA-2025:11298
  • Red Hat Enterprise Linux NFV (v. 8) kernel-rt 4.18.0-553.62.1.rt7.403.el8_10, kernel-rt-kvm 4.18.0-553.62.1.rt7.403.el8_10, kernel-rt-core 4.18.0-553.62.1.rt7.403.el8_10, kernel-rt-modules 4.18.0-553.62.1.rt7.403.el8_10, kernel-rt-debug-kvm 4.18.0-553.62.1.rt7.403.el8_10, kernel-rt-debug-core 4.18.0-553.62.1.rt7.403.el8_10, +4 more
    fixed: vendor fix RHSA-2025:11299
  • Red Hat Enterprise Linux NFV E4S (v.9.0) kernel-rt 5.14.0-70.142.1.rt21.214.el9_0, kernel-rt-kvm 5.14.0-70.142.1.rt21.214.el9_0, kernel-rt-core 5.14.0-70.142.1.rt21.214.el9_0, kernel-rt-modules 5.14.0-70.142.1.rt21.214.el9_0, kernel-rt-debug-kvm 5.14.0-70.142.1.rt21.214.el9_0, kernel-rt-debug-core 5.14.0-70.142.1.rt21.214.el9_0, +4 more
    fixed: vendor fix RHSA-2025:14094
  • Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-570.26.1.el9_6, kernel-rt-64k 5.14.0-570.26.1.el9_6, kernel-rt-core 5.14.0-570.26.1.el9_6, kernel-rt-modules 5.14.0-570.26.1.el9_6, kernel-rt-64k-core 5.14.0-570.26.1.el9_6, kernel-rt-debug-core 5.14.0-570.26.1.el9_6, +14 more
    fixed: vendor fix RHSA-2025:10837
  • Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-55.20.1.el10_0, kernel-rt-64k 6.12.0-55.20.1.el10_0, kernel-rt-core 6.12.0-55.20.1.el10_0, kernel-rt-modules 6.12.0-55.20.1.el10_0, kernel-rt-64k-core 6.12.0-55.20.1.el10_0, kernel-rt-debug-core 6.12.0-55.20.1.el10_0, +14 more
    fixed: vendor fix RHSA-2025:10371
  • Red Hat Enterprise Linux Real Time E4S (v.9.0) kernel-rt 5.14.0-70.142.1.rt21.214.el9_0, kernel-rt-core 5.14.0-70.142.1.rt21.214.el9_0, kernel-rt-modules 5.14.0-70.142.1.rt21.214.el9_0, kernel-rt-debug-core 5.14.0-70.142.1.rt21.214.el9_0, kernel-rt-debug-modules 5.14.0-70.142.1.rt21.214.el9_0, kernel-rt-modules-extra 5.14.0-70.142.1.rt21.214.el9_0, +2 more
    fixed: vendor fix RHSA-2025:14094
  • Red Hat Enterprise Linux Real Time E4S (v.9.2) kernel-rt 5.14.0-284.130.1.rt14.415.el9_2, kernel-rt-core 5.14.0-284.130.1.rt14.415.el9_2, kernel-rt-modules 5.14.0-284.130.1.rt14.415.el9_2, kernel-rt-debug-core 5.14.0-284.130.1.rt14.415.el9_2, kernel-rt-modules-core 5.14.0-284.130.1.rt14.415.el9_2, kernel-rt-debug-modules 5.14.0-284.130.1.rt14.415.el9_2, +4 more
    fixed: vendor fix RHSA-2025:13633
  • Red Hat Enterprise Linux Real Time EUS (v.9.4) kernel-rt 5.14.0-427.81.1.el9_4, kernel-rt-core 5.14.0-427.81.1.el9_4, kernel-rt-modules 5.14.0-427.81.1.el9_4, kernel-rt-debug-core 5.14.0-427.81.1.el9_4, kernel-rt-modules-core 5.14.0-427.81.1.el9_4, kernel-rt-debug-modules 5.14.0-427.81.1.el9_4, +4 more
    fixed: vendor fix RHSA-2025:13135
  • Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-570.26.1.el9_6, kernel-rt-kvm 5.14.0-570.26.1.el9_6, kernel-rt-core 5.14.0-570.26.1.el9_6, kernel-rt-modules 5.14.0-570.26.1.el9_6, kernel-rt-debug-kvm 5.14.0-570.26.1.el9_6, kernel-rt-debug-core 5.14.0-570.26.1.el9_6, +6 more
    fixed: vendor fix RHSA-2025:10837
  • Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-55.20.1.el10_0, kernel-rt-kvm 6.12.0-55.20.1.el10_0, kernel-rt-core 6.12.0-55.20.1.el10_0, kernel-rt-modules 6.12.0-55.20.1.el10_0, kernel-rt-debug-kvm 6.12.0-55.20.1.el10_0, kernel-rt-debug-core 6.12.0-55.20.1.el10_0, +6 more
    fixed: vendor fix RHSA-2025:10371
  • Red Hat Enterprise Linux Real Time for NFV E4S (v.9.2) kernel-rt 5.14.0-284.130.1.rt14.415.el9_2, kernel-rt-kvm 5.14.0-284.130.1.rt14.415.el9_2, kernel-rt-core 5.14.0-284.130.1.rt14.415.el9_2, kernel-rt-modules 5.14.0-284.130.1.rt14.415.el9_2, kernel-rt-debug-kvm 5.14.0-284.130.1.rt14.415.el9_2, kernel-rt-debug-core 5.14.0-284.130.1.rt14.415.el9_2, +6 more
    fixed: vendor fix RHSA-2025:13633
  • Red Hat Enterprise Linux Real Time for NFV EUS (v.9.4) kernel-rt 5.14.0-427.81.1.el9_4, kernel-rt-kvm 5.14.0-427.81.1.el9_4, kernel-rt-core 5.14.0-427.81.1.el9_4, kernel-rt-modules 5.14.0-427.81.1.el9_4, kernel-rt-debug-kvm 5.14.0-427.81.1.el9_4, kernel-rt-debug-core 5.14.0-427.81.1.el9_4, +6 more
    fixed: vendor fix RHSA-2025:13135
  • Red Hat Enterprise Linux RT (v. 8) kernel-rt 4.18.0-553.62.1.rt7.403.el8_10, kernel-rt-core 4.18.0-553.62.1.rt7.403.el8_10, kernel-rt-modules 4.18.0-553.62.1.rt7.403.el8_10, kernel-rt-debug-core 4.18.0-553.62.1.rt7.403.el8_10, kernel-rt-debug-modules 4.18.0-553.62.1.rt7.403.el8_10, kernel-rt-modules-extra 4.18.0-553.62.1.rt7.403.el8_10, +2 more
    fixed: vendor fix RHSA-2025:11299
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 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
total
Assessed
13 mo ago

Exploit prediction

0.22% chance of exploitation in the next 30 days, higher than 13% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

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

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.