{
  "cveId": "CVE-2026-31397",
  "url": "https://patchblox.com/security/cve/CVE-2026-31397",
  "summary": "CVE-2026-31397 is fixed in 23 products on 1 platform, first by DEBIAN-CVE-2026-31397, released April 3, 2026. It is not reported as exploited. Patch Radar priority: High.",
  "title": "linux: In the Linux kernel, the following vulnerability has been resolved:  mm/huge_memory: fix use of NULL folio in move_pa...",
  "description": "In the Linux kernel, the following vulnerability has been resolved:  mm/huge_memory: fix use of NULL folio in move_pages_huge_pmd()  move_pages_huge_pmd() handles UFFDIO_MOVE for both normal THPs and huge zero pages.  For the huge zero page path, src_folio is explicitly set to NULL, and is used as a sentinel to skip folio operations like lock and rmap.  In the huge zero page branch, src_folio is NULL, so folio_mk_pmd(NULL, pgprot) passes NULL through folio_pfn() and page_to_pfn().  With SPARSEMEM_VMEMMAP this silently produces a bogus PFN, installing a PMD pointing to non-existent physical memory.  On other memory models it is a NULL dereference.  Use page_folio(src_page) to obtain the valid huge zero folio from the page, which was obtained from pmd_page() and remains valid throughout.  After commit d82d09e48219 (\u0022mm/huge_memory: mark PMD mappings of the huge zero folio special\u0022), moved huge zero PMDs must remain special so vm_normal_page_pmd() continues to treat them as special mappings.  move_pages_huge_pmd() currently reconstructs the destination PMD in the huge zero page branch, which drops PMD state such as pmd_special() on architectures with CONFIG_ARCH_HAS_PTE_SPECIAL.  As a result, vm_normal_page_pmd() can treat the moved huge zero PMD as a normal page and corrupt its refcount.  Instead of reconstructing the PMD from the folio, derive the destination entry from src_pmdval after pmdp_huge_clear_flush(), then handle the PMD metadata the same way move_huge_pmd() does for moved entries by marking it soft-dirty and clearing uffd-wp.",
  "published": "2026-04-03T16:16:38Z",
  "severity": "high",
  "cvss": 7.8,
  "cvssVector": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
  "epss": 0.00123,
  "epssPercentile": 0.02093,
  "priority": "High",
  "priorityTier": 3,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "fixes": [
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      "release": "amzn 2023",
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      "fix": "ALAS2023-2026-1596",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-1596",
      "released": "2026-04-27T09:00:00Z"
    },
    {
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      "fix": "ALAS2023-2026-1596",
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      "released": "2026-04-27T09:00:00Z"
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    },
    {
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  ],
  "noFixYet": [],
  "dataAsOf": "2026-11-08T00:53:09Z",
  "attribution": {
    "text": "Data: Patchblox Patch Radar",
    "url": "https://patchblox.com/security/patch-radar",
    "terms": "https://patchblox.com/security/patch-radar/use-the-data"
  }
}