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CVE-2025-21991 is an out-of-bounds access in the Linux kernel x86 AMD microcode-loading path, specifically load_microcode_amd(). The vulnerable logic iterates over all NUMA nodes and accesses per-CPU data for the first CPU in each node's CPU mask without verifying that the mask contains a CPU. On systems with CPU-less NUMA nodes, including far-memory configurations, the empty mask causes cpumask_first() to return CONFIG_NR_CPUS, resulting in an access one index beyond the cpu_info per-CPU array while an AMD microcode update is flashed. The upstream correction restricts processing to NUMA nodes that contain CPUs.
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No public exploit code observed for this vulnerability.
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Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
14 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An out-of-bounds vulnerability in the Linux kernel's AMD x86 microcode handling on systems with CPU-less NUMA nodes, affecting Rocky Linux 10.0 kernel packages covered by CIQ advisory crlsa-2025_10371.
An out-of-bounds vulnerability in the Linux kernel's x86 AMD microcode handling on systems with CPU-less NUMA nodes.
An out-of-bounds vulnerability in Linux kernel AMD x86 microcode handling on systems with CPU-less NUMA nodes.
An out-of-bounds vulnerability in Linux kernel AMD x86 microcode handling on systems with CPU-less NUMA nodes.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.