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userfaultfd: gate must_wait writability check on pte_present()

Type: advisorySources: OSV

In the Linux kernel, the following vulnerability has been resolved: userfaultfd: gate must_wait writability check on pte_present() userfaultfd_must_wait() and userfaultfd_huge_must_wait() read the PTE without taking the page table lock and then apply pte_write() / huge_pte_write() to it. Those accessors decode bits from the present encoding only; on a swap or migration entry they read the offset bits that happen to share the same position and return an undefined result. The intent of the check is "is this fault still WP-blocked?". A non-marker swap entry means the page is in transit -- the userfault context the original fault delivered against is no longer the same, and the swap-in or migration completion path will re-deliver a fresh fault if userspace still needs to handle it. Worst case under the current code the garbage write bit says "wait", and the thread stays asleep until a UFFDIO_WAKE that may never arrive. Gate the writability check on pte_present() so the lockless re-check only inspects present-PTE bits when the entry is actually present. The non-present, non-marker case returns "don't wait" and lets the fault path retry.

Products
Kernel
Affected versions
Not specified
Fixed versions
5.10.261, 5.15.212, 6.1.178, 6.12.96, 6.18.39, 6.6.145, 7.1.4
CVEs
CVE-2026-64514
Confirmed fixed CVEs
Not specified
Updated in this feed
4 Nov 2026, 14:09 UTC · Revision 1

Source evidence

userfaultfd: gate must_wait writability check on pte_present()

core-osv · Original source

Published 25 Jul 2026, 08:52 UTC

In the Linux kernel, the following vulnerability has been resolved: userfaultfd: gate must_wait writability check on pte_present() userfaultfd_must_wait() and userfaultfd_huge_must_wait() read the PTE without taking the page table lock and then apply pte_write() / huge_pte_write() to it. Those accessors decode bits from the present encoding only; on a swap or migration entry they read the offset bits that happen to share the same position and return an undefined result. The intent of the check is "is this fault still WP-blocked?". A non-marker swap entry means the page is in transit -- the userfault context the original fault delivered against is no longer the same, and the swap-in or migration completion path will re-deliver a fresh fault if userspace still needs to handle it. Worst case under the current code the garbage write bit says "wait", and the thread stays asleep until a UFFDIO_WAKE that may never arrive. Gate the writability check on pte_present() so the lockless re-check only inspects present-PTE bits when the entry is actually present. The non-present, non-marker case returns "don't wait" and lets the fault path retry.

osv:CVE-2026-64514

Kernel

Fixed versions: 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.96, 6.18.39, 7.1.4

Complete source record
{
  "id": "1e7027646c28346829197d37af47c1c5b5cdd3f1a14623744ce86f7eb31e3b10",
  "url": "https://osv.dev/vulnerability/CVE-2026-64514",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "userfaultfd: gate must_wait writability check on pte_present()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: userfaultfd: gate must_wait writability check on pte_present() userfaultfd_must_wait() and userfaultfd_huge_must_wait() read the PTE without taking the page table lock and then apply pte_write() / huge_pte_write() to it. Those accessors decode bits from the present encoding only; on a swap or migration entry they read the offset bits that happen to share the same position and return an undefined result. The intent of the check is \"is this fault still WP-blocked?\". A non-marker swap entry means the page is in transit -- the userfault context the original fault delivered against is no longer the same, and the swap-in or migration completion path will re-deliver a fresh fault if userspace still needs to handle it. Worst case under the current code the garbage write bit says \"wait\", and the thread stays asleep until a UFFDIO_WAKE that may never arrive. Gate the writability check on pte_present() so the lockless re-check only inspects present-PTE bits when the entry is actually present. The non-present, non-marker case returns \"don't wait\" and lets the fault path retry.",
    "evidence": "osv:CVE-2026-64514",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "5.10.261",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "5.15.212",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.1.178",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.145",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.96",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.39",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.1.4",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-64514",
      "aliases": [
        "CVE-2026-64514"
      ],
      "affected": [
        {
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            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                {
                  "fixed": "a5700a4c1c9099ac2ac73fe8a09cf059972e0d2f"
                },
                {
                  "fixed": "d4026417e8184d13850a0bad4d96ceb6ed9f7152"
                },
                {
                  "fixed": "29e6f952c5fb7dc1d6b90fe5b7f36063d44ddae0"
                },
                {
                  "fixed": "5f4dbdb0a87596214076b20b94f2b71b522170b3"
                },
                {
                  "fixed": "a6e9a4939e359599701b1da351e84f72e021443a"
                },
                {
                  "fixed": "60d696a037eeeedfb57756dfe7ec08a1587c8631"
                },
                {
                  "fixed": "710183888174639a15fcec16cd1af766b8480bb7"
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                {
                  "fixed": "8e80af52db652fbc41320eee45a4f73bc029faf2"
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        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "4.11.0"
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                {
                  "fixed": "5.10.261"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.11.0"
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                {
                  "fixed": "5.15.212"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.16.0"
                },
                {
                  "fixed": "6.1.178"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.2.0"
                },
                {
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
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                {
                  "fixed": "6.12.96"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
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                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.18.39"
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            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
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          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64514.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:35.947240079Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/29e6f952c5fb7dc1d6b90fe5b7f36063d44ddae0",
        "https://git.kernel.org/stable/c/5f4dbdb0a87596214076b20b94f2b71b522170b3",
        "https://git.kernel.org/stable/c/60d696a037eeeedfb57756dfe7ec08a1587c8631",
        "https://git.kernel.org/stable/c/710183888174639a15fcec16cd1af766b8480bb7",
        "https://git.kernel.org/stable/c/8e80af52db652fbc41320eee45a4f73bc029faf2",
        "https://git.kernel.org/stable/c/a5700a4c1c9099ac2ac73fe8a09cf059972e0d2f",
        "https://git.kernel.org/stable/c/a6e9a4939e359599701b1da351e84f72e021443a",
        "https://git.kernel.org/stable/c/d4026417e8184d13850a0bad4d96ceb6ed9f7152",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64514.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-64514",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64514.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-64514",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 503461,
  "published_at": "2026-07-25T08:52:05.878+00:00"
}