CVE-2026-31397

Estado: AnalizadaAlta (7.8)—

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.

Leer descripción completaMostrar menos

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 ("mm/huge_memory: mark PMD mappings of the huge zero folio special"), 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.

CVSS

Versión: 3.1
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Puntuación base: 7.8

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.17%
Percentil entre todas las CVEs puntuadas: 6
Fecha de la puntuación: 4/10/2026

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

ExplotaciónT1068 Exploitation for Privilege Escalationprivilege escalation85 %
Impacto principalT1059 Command and Scripting Interpreterexecution70 %
Impacto secundarioT1565.001 Stored Data Manipulationimpact75 %

Vector CVSS AV:L/PR:L/UI:N indica escalada local sin interacción (T1068). La corrupción de memoria y refcount permite ejecución de código (T1059) y manipulación de datos del sistema (T1565.001).

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Execution Prevention Threat Intelligence Program Restrict Web-Based Content Restrict File and Directory Permissions Privileged Account Management Remote Data Storage

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

CWE-476

Referencias

JSON original (NVD)

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      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm/huge_memory: fix use of NULL folio in move_pages_huge_pmd()\n\nmove_pages_huge_pmd() handles UFFDIO_MOVE for both normal THPs and huge\nzero pages.  For the huge zero page path, src_folio is explicitly set to\nNULL, and is used as a sentinel to skip folio operations like lock and\nrmap.\n\nIn the huge zero page branch, src_folio is NULL, so folio_mk_pmd(NULL,\npgprot) passes NULL through folio_pfn() and page_to_pfn().  With\nSPARSEMEM_VMEMMAP this silently produces a bogus PFN, installing a PMD\npointing to non-existent physical memory.  On other memory models it is a\nNULL dereference.\n\nUse page_folio(src_page) to obtain the valid huge zero folio from the\npage, which was obtained from pmd_page() and remains valid throughout.\n\nAfter commit d82d09e48219 (\"mm/huge_memory: mark PMD mappings of the huge\nzero folio special\"), moved huge zero PMDs must remain special so\nvm_normal_page_pmd() continues to treat them as special mappings.\n\nmove_pages_huge_pmd() currently reconstructs the destination PMD in the\nhuge zero page branch, which drops PMD state such as pmd_special() on\narchitectures with CONFIG_ARCH_HAS_PTE_SPECIAL.  As a result,\nvm_normal_page_pmd() can treat the moved huge zero PMD as a normal page\nand corrupt its refcount.\n\nInstead of reconstructing the PMD from the folio, derive the destination\nentry from src_pmdval after pmdp_huge_clear_flush(), then handle the PMD\nmetadata the same way move_huge_pmd() does for moved entries by marking it\nsoft-dirty and clearing uffd-wp."
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      "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nmm/huge_memory: corrige el uso de folio NULL en move_pages_huge_pmd()\n\nmove_pages_huge_pmd() maneja UFFDIO_MOVE tanto para THPs normales como para páginas cero enormes. Para la ruta de la página cero enorme, src_folio se establece explícitamente en NULL, y se usa como un centinela para omitir operaciones de folio como lock y rmap.\n\nEn la rama de la página cero enorme, src_folio es NULL, por lo que folio_mk_pmd(NULL, pgprot) pasa NULL a través de folio_pfn() y page_to_pfn(). Con SPARSEMEM_VMEMMAP esto produce silenciosamente un PFN erróneo, instalando un PMD que apunta a memoria física inexistente. En otros modelos de memoria es una desreferencia NULL.\n\nUsar page_folio(src_page) para obtener el folio cero enorme válido de la página, que se obtuvo de pmd_page() y permanece válido en todo momento.\n\nDespués del commit d82d09e48219 ('mm/huge_memory: marcar las asignaciones PMD del folio cero enorme como especiales'), los PMD cero enormes movidos deben permanecer especiales para que vm_normal_page_pmd() continúe tratándolos como asignaciones especiales.\n\nmove_pages_huge_pmd() actualmente reconstruye el PMD de destino en la rama de la página cero enorme, lo que elimina el estado del PMD como pmd_special() en arquitecturas con CONFIG_ARCH_HAS_PTE_SPECIAL. Como resultado, vm_normal_page_pmd() puede tratar el PMD cero enorme movido como una página normal y corromper su refcount.\n\nEn lugar de reconstruir el PMD a partir del folio, derivar la entrada de destino de src_pmdval después de pmdp_huge_clear_flush(), luego manejar los metadatos del PMD de la misma manera que move_huge_pmd() lo hace para las entradas movidas, marcándolo como soft-dirty y borrando uffd-wp."
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  "lastModified": "2026-07-24T22:10:00.140",
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