{
  "threat_severity" : "Moderate",
  "public_date" : "2025-04-02T00:00:00Z",
  "bugzilla" : {
    "description" : "kernel: x86/microcode/AMD: Fix out-of-bounds on systems with CPU-less NUMA nodes",
    "id" : "2356917",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2356917"
  },
  "cvss3" : {
    "cvss3_base_score" : "6.7",
    "cvss3_scoring_vector" : "CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H",
    "status" : "verified"
  },
  "cwe" : "CWE-787",
  "details" : [ "In the Linux kernel, the following vulnerability has been resolved:\nx86/microcode/AMD: Fix out-of-bounds on systems with CPU-less NUMA nodes\nCurrently, load_microcode_amd() iterates over all NUMA nodes, retrieves their\nCPU masks and unconditionally accesses per-CPU data for the first CPU of each\nmask.\nAccording to Documentation/admin-guide/mm/numaperf.rst:\n\"Some memory may share the same node as a CPU, and others are provided as\nmemory only nodes.\"\nTherefore, some node CPU masks may be empty and wouldn't have a \"first CPU\".\nOn a machine with far memory (and therefore CPU-less NUMA nodes):\n- cpumask_of_node(nid) is 0\n- cpumask_first(0) is CONFIG_NR_CPUS\n- cpu_data(CONFIG_NR_CPUS) accesses the cpu_info per-CPU array at an\nindex that is 1 out of bounds\nThis does not have any security implications since flashing microcode is\na privileged operation but I believe this has reliability implications by\npotentially corrupting memory while flashing a microcode update.\nWhen booting with CONFIG_UBSAN_BOUNDS=y on an AMD machine that flashes\na microcode update. I get the following splat:\nUBSAN: array-index-out-of-bounds in arch/x86/kernel/cpu/microcode/amd.c:X:Y\nindex 512 is out of range for type 'unsigned long[512]'\n[...]\nCall Trace:\ndump_stack\n__ubsan_handle_out_of_bounds\nload_microcode_amd\nrequest_microcode_amd\nreload_store\nkernfs_fop_write_iter\nvfs_write\nksys_write\ndo_syscall_64\nentry_SYSCALL_64_after_hwframe\nChange the loop to go over only NUMA nodes which have CPUs before determining\nwhether the first CPU on the respective node needs microcode update.\n[ bp: Massage commit message, fix typo. ]" ],
  "statement" : "This vulnerability requires elevated privileges (e.g. `CAP_SYS_ADMIN`) to be triggered as the attacker needs to be able to initiate a microcode update. This action is highly privileged, as it involves writing directly to the CPU, and so cannot be done by a regular, unprivileged user.",
  "affected_release" : [ {
    "product_name" : "Red Hat Enterprise Linux 10",
    "release_date" : "2025-07-07T00:00:00Z",
    "advisory" : "RHSA-2025:10371",
    "cpe" : "cpe:/o:redhat:enterprise_linux:10.0",
    "package" : "kernel-0:6.12.0-55.20.1.el10_0"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8",
    "release_date" : "2025-07-16T00:00:00Z",
    "advisory" : "RHSA-2025:11299",
    "cpe" : "cpe:/a:redhat:enterprise_linux:8::nfv",
    "package" : "kernel-rt-0:4.18.0-553.62.1.rt7.403.el8_10"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8",
    "release_date" : "2025-07-16T00:00:00Z",
    "advisory" : "RHSA-2025:11298",
    "cpe" : "cpe:/o:redhat:enterprise_linux:8",
    "package" : "kernel-0:4.18.0-553.62.1.el8_10"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9",
    "release_date" : "2025-07-14T00:00:00Z",
    "advisory" : "RHSA-2025:10837",
    "cpe" : "cpe:/a:redhat:enterprise_linux:9",
    "package" : "kernel-0:5.14.0-570.26.1.el9_6"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9",
    "release_date" : "2025-07-14T00:00:00Z",
    "advisory" : "RHSA-2025:10837",
    "cpe" : "cpe:/o:redhat:enterprise_linux:9",
    "package" : "kernel-0:5.14.0-570.26.1.el9_6"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9.0 Update Services for SAP Solutions",
    "release_date" : "2025-08-19T00:00:00Z",
    "advisory" : "RHSA-2025:14054",
    "cpe" : "cpe:/a:redhat:rhel_e4s:9.0",
    "package" : "kernel-0:5.14.0-70.142.1.el9_0"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9.0 Update Services for SAP Solutions",
    "release_date" : "2025-08-19T00:00:00Z",
    "advisory" : "RHSA-2025:14094",
    "cpe" : "cpe:/a:redhat:rhel_e4s:9.0::nfv",
    "package" : "kernel-rt-0:5.14.0-70.142.1.rt21.214.el9_0"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions",
    "release_date" : "2025-08-13T00:00:00Z",
    "advisory" : "RHSA-2025:13781",
    "cpe" : "cpe:/a:redhat:rhel_e4s:9.2",
    "package" : "kernel-0:5.14.0-284.130.1.el9_2"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions",
    "release_date" : "2025-08-11T00:00:00Z",
    "advisory" : "RHSA-2025:13633",
    "cpe" : "cpe:/a:redhat:rhel_e4s:9.2::nfv",
    "package" : "kernel-rt-0:5.14.0-284.130.1.rt14.415.el9_2"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9.4 Extended Update Support",
    "release_date" : "2025-08-06T00:00:00Z",
    "advisory" : "RHSA-2025:13135",
    "cpe" : "cpe:/a:redhat:rhel_eus:9.4",
    "package" : "kernel-0:5.14.0-427.81.1.el9_4"
  } ],
  "package_state" : [ {
    "product_name" : "Red Hat Enterprise Linux 6",
    "fix_state" : "Not affected",
    "package_name" : "kernel",
    "cpe" : "cpe:/o:redhat:enterprise_linux:6"
  }, {
    "product_name" : "Red Hat Enterprise Linux 7",
    "fix_state" : "Not affected",
    "package_name" : "kernel",
    "cpe" : "cpe:/o:redhat:enterprise_linux:7"
  }, {
    "product_name" : "Red Hat Enterprise Linux 7",
    "fix_state" : "Not affected",
    "package_name" : "kernel-rt",
    "cpe" : "cpe:/o:redhat:enterprise_linux:7"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9",
    "fix_state" : "Affected",
    "package_name" : "kernel-rt",
    "cpe" : "cpe:/o:redhat:enterprise_linux:9"
  } ],
  "references" : [ "https://www.cve.org/CVERecord?id=CVE-2025-21991\nhttps://nvd.nist.gov/vuln/detail/CVE-2025-21991\nhttps://lore.kernel.org/linux-cve-announce/2025040257-CVE-2025-21991-6aae@gregkh/T" ],
  "name" : "CVE-2025-21991",
  "csaw" : false
}