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CVE-2025-21991— x86/microcode/AMD: Fix out-of-bounds on systems with CPU-less NUMA nodes

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于x86/microcode/AMD组件在无CPU的NUMA节点上可能越界访问。

AI Predicted 3.3 Difficulty: Hard EPSS 0.22% · P12

Possible ATT&CK Techniques 1 AI

T1068 · Exploitation for Privilege Escalation

Affected Version Matrix 28

VendorProduct Version RangeStatus
Linux Linux 979e197968a1e8f09bf0d706801dba4432f85ab3< d509c4731090ebd9bbdb72c70a2d70003ae81f4f affected
44a44b57e88f311c1415be1f567c50050913c149< 985a536e04bbfffb1770df43c6470f635a6b1073 affected
be2710deaed3ab1402379a2ede30a3754fe6767a< 18b5d857c6496b78ead2fd10001b81ae32d30cac affected
d576547f489c935b9897d4acf8beee3325dea8a5< ec52240622c4d218d0240079b7c1d3ec2328a9f4 affected
7ff6edf4fef38ab404ee7861f257e28eaaeed35f< e686349cc19e800dac8971929089ba5ff59abfb0 affected
7ff6edf4fef38ab404ee7861f257e28eaaeed35f< 488ffc0cac38f203979f83634236ee53251ce593 affected
7ff6edf4fef38ab404ee7861f257e28eaaeed35f< 5ac295dfccb5b015493f86694fa13a0dde4d3665 affected
7ff6edf4fef38ab404ee7861f257e28eaaeed35f< e3e89178a9f4a80092578af3ff3c8478f9187d59 affected
… +20 more rows
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I. Basic Information for CVE-2025-21991

Vulnerability Information
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Vulnerability Title
x86/microcode/AMD: Fix out-of-bounds on systems with CPU-less NUMA nodes
Source: CVE Program / CVE List V5
Vulnerability Description
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. ]
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于x86/microcode/AMD组件在无CPU的NUMA节点上可能越界访问。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 979e197968a1e8f09bf0d706801dba4432f85ab3 ~ d509c4731090ebd9bbdb72c70a2d70003ae81f4f -
Linux Linux 6.3 -

II. Public POCs for CVE-2025-21991

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III. Intelligence Information for CVE-2025-21991

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Patches & Fixes for CVE-2025-21991 (3)

Same Patch Batch · Linux · 2025-04-02 · 8 CVEs total

CVE-2025-21988 9.8 CRITICAL fs/netfs/read_collect: add to next->prev_donated
CVE-2025-21994 7.6 HIGH ksmbd: fix incorrect validation for num_aces field of smb_acl
CVE-2025-21993 iscsi_ibft: Fix UBSAN shift-out-of-bounds warning in ibft_attr_show_nic()
CVE-2025-21992 HID: ignore non-functional sensor in HP 5MP Camera
CVE-2025-21990 drm/amdgpu: NULL-check BO's backing store when determining GFX12 PTE flags
CVE-2025-21989 drm/amd/display: fix missing .is_two_pixels_per_container
CVE-2025-21987 drm/amdgpu: init return value in amdgpu_ttm_clear_buffer

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux