HighFix available
x86/microcode/AMD: Fix out-of-bounds on systems with CPU-less NUMA nodes
Type: advisorySources: OSV
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
- Products
- Kernel
- Affected versions
- Not specified
- Fixed versions
- 5.10.236, 5.15.180, 5.4.292, 6.1.132, 6.12.20, 6.13.8, 6.6.84
- CVEs
- CVE-2025-21991
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 3 Nov 2026, 05:19 UTC · Revision 1
Source evidence
x86/microcode/AMD: Fix out-of-bounds on systems with CPU-less NUMA nodes
core-osv · Original sourcePublished 2 Apr 2025, 12:53 UTC
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
osv:CVE-2025-21991
Kernel
Fixed versions: 5.4.292, 5.10.236, 5.15.180, 6.1.132, 6.6.84, 6.12.20, 6.13.8
Complete source record
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}
]
},
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "6.2.0"
},
{
"fixed": "6.6.84"
}
]
},
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "6.3.0"
},
{
"fixed": "6.12.20"
}
]
},
{
"type": "ECOSYSTEM",
"events": [
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},
{
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}
]
}
],
"package": {
"name": "Kernel",
"ecosystem": "Linux"
},
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-21991.json"
}
}
],
"modified": "2026-10-28T02:30:26.294851591Z",
"provider": "osv",
"references": [
"https://git.kernel.org/stable/c/18b5d857c6496b78ead2fd10001b81ae32d30cac",
"https://git.kernel.org/stable/c/488ffc0cac38f203979f83634236ee53251ce593",
"https://git.kernel.org/stable/c/5ac295dfccb5b015493f86694fa13a0dde4d3665",
"https://git.kernel.org/stable/c/985a536e04bbfffb1770df43c6470f635a6b1073",
"https://git.kernel.org/stable/c/d509c4731090ebd9bbdb72c70a2d70003ae81f4f",
"https://git.kernel.org/stable/c/e3e89178a9f4a80092578af3ff3c8478f9187d59",
"https://git.kernel.org/stable/c/e686349cc19e800dac8971929089ba5ff59abfb0",
"https://git.kernel.org/stable/c/ec52240622c4d218d0240079b7c1d3ec2328a9f4",
"https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html",
"https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html",
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/21xxx/CVE-2025-21991.json",
"https://nvd.nist.gov/vuln/detail/CVE-2025-21991",
"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
],
"provider_metadata": {
"cna_assigner": "Linux",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/21xxx/CVE-2025-21991.json"
}
},
"related_cves": [
{
"value": "CVE-2025-21991",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 492682,
"published_at": "2025-04-02T12:53:14.23+00:00"
}