{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-31397", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-03-09T15:48:24.085Z", "datePublished": "2026-04-03T15:16:01.427Z", "dateUpdated": "2026-08-05T12:22:06.974Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T12:22:06.974Z" }, "descriptions": [ { "lang": "en", "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." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:L - The vulnerable path is reached through local `userfaultfd` ioctls, specifically `UFFDIO_MOVE`, on the attacker's own address space.\nAC:L - An attacker can create aligned anonymous VMAs, materialize a huge zero PMD with reads, register the destination with userfaultfd, and issue `UFFDIO_MOVE`; no uncontrollable race is required.\nPR:L - A basic unprivileged local user can create a userspace-only userfaultfd with `UFFD_USER_MODE_ONLY` and exercise `UFFDIO_MOVE` on their own memory.\nUI:N - Exploitation is driven entirely by the attacker's own syscalls and memory accesses and does not require a victim user action.\nS:U - The impact is within the local kernel and the attacking process's memory-management context, with no separate security authority crossed.\nC:H - The bug can install a malformed huge PMD and the fix notes refcount corruption when huge zero PMDs lose special state; treating this as kernel memory corruption makes high confidentiality impact defensible.\nI:H - The malformed PMD/refcount corruption affects kernel-managed memory structures and can plausibly be developed beyond a crash into memory modification or control-flow compromise.\nA:H - On some memory models this is a direct NULL dereference, and on common sparse-vmemmap systems it installs a bogus PMD that can crash the kernel during access or later VM teardown." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "mm/huge_memory.c" ], "versions": [ { "version": "e3981db444a0a18d350d9f92e3f2e8d489b54211", "lessThan": "f3caaee0f9e489fd2282d4ce45791dc8aed2da62", "status": "affected", "versionType": "git" }, { "version": "e3981db444a0a18d350d9f92e3f2e8d489b54211", "lessThan": "e3133d0986dc5a231d5419167dbac65312b28b41", "status": "affected", "versionType": "git" }, { "version": "e3981db444a0a18d350d9f92e3f2e8d489b54211", "lessThan": "fae654083bfa409bb2244f390232e2be47f05bfc", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "mm/huge_memory.c" ], "versions": [ { "version": "6.16", "status": "affected" }, { "version": "0", "lessThan": "6.16", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.20", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.19.10", "lessThanOrEqual": "6.19.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.0", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.16", "versionEndExcluding": "6.18.20" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.16", "versionEndExcluding": "6.19.10" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.16", "versionEndExcluding": "7.0" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/f3caaee0f9e489fd2282d4ce45791dc8aed2da62" }, { "url": "https://git.kernel.org/stable/c/e3133d0986dc5a231d5419167dbac65312b28b41" }, { "url": "https://git.kernel.org/stable/c/fae654083bfa409bb2244f390232e2be47f05bfc" } ], "title": "mm/huge_memory: fix use of NULL folio in move_pages_huge_pmd()", "x_generator": { "engine": "bippy-1.2.0" } } } }