Detections
Analytics

Azure Linux 3.0 Security Update: kernel (CVE-2025-21991)

high Nessus Plugin ID 295499

Synopsis

The remote Azure Linux host is missing one or more security updates.

Description

The version of kernel installed on the remote Azure Linux 3.0 host is prior to tested version. It is, therefore, affected by a vulnerability as referenced in the CVE-2025-21991 advisory.

 - 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. ] (CVE-2025-21991)

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

Solution

Update the affected packages.

See Also

https://nvd.nist.gov/vuln/detail/CVE-2025-21991

Plugin Details

Severity: High

ID: 295499

File Name: azure_linux_CVE-2025-21991.nasl

Version: 1.1

Type: local

Published: 1/22/2026

Updated: 1/22/2026

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 6.7

CVSS v2

Risk Factor: Medium

Base Score: 6.8

Temporal Score: 5

Vector: CVSS2#AV:L/AC:L/Au:S/C:C/I:C/A:C

CVSS Score Source: CVE-2025-21991

CVSS v3

Risk Factor: High

Base Score: 7.8

Temporal Score: 6.8

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

CPE: p-cpe:/a:microsoft:azure_linux:kernel-tools, p-cpe:/a:microsoft:azure_linux:kernel-devel, p-cpe:/a:microsoft:azure_linux:kernel-debuginfo, p-cpe:/a:microsoft:azure_linux:kernel-docs, p-cpe:/a:microsoft:azure_linux:kernel-drivers-intree-amdgpu, p-cpe:/a:microsoft:azure_linux:bpftool, p-cpe:/a:microsoft:azure_linux:python3-perf, p-cpe:/a:microsoft:azure_linux:kernel-drivers-gpu, x-cpe:/o:microsoft:azure_linux, p-cpe:/a:microsoft:azure_linux:kernel-drivers-sound, p-cpe:/a:microsoft:azure_linux:kernel, p-cpe:/a:microsoft:azure_linux:kernel-drivers-accessibility

Required KB Items: Host/local_checks_enabled, Host/cpu, Host/AzureLinux/release, Host/AzureLinux/rpm-list

Exploit Ease: No known exploits are available

Patch Publication Date: 5/13/2025

Vulnerability Publication Date: 4/2/2025

Reference Information

CVE: CVE-2025-21991