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Fencer Vulns
high 7.8

CVE-2026-64181 json

mm: fix __vm_normal_page() to handle missing support for pmd_special()/pud_special()

published 2026-07-19 3 mo ago modified 2026-08-11 2 mo ago also EUVD-2026-45866

cvss
7.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 6%
public exploits
0
none known

Summary

In the Linux kernel, the following vulnerability has been resolved:

mm: fix __vm_normal_page() to handle missing support for pmd_special()/pud_special()

On x86 32-bit with THP enabled, zap_huge_pmd() is seen to generate a "WARNING: mm/memory.c:735 at __vm_normal_page+0x6a/0x7d", from the VM_WARN_ON_ONCE(is_zero_pfn(pfn) || is_huge_zero_pfn(pfn)); followed by "BUG: Bad rss-counter state"s, then later "BUG: Bad page state"s when reclaim gets to call shrink_huge_zero_folio_scan().

It's as if the _PAGE_SPECIAL bit never got set in the huge_zero pmd: and indeed, whereas pte_special() and pte_mkspecial() are subject to a dedicated CONFIG_ARCH_HAS_PTE_SPECIAL, pmd_special() and pmd_mkspecial() are subject to CONFIG_ARCH_SUPPORTS_PMD_PFNMAP, which is never enabled on any 32-bit architecture.

While the problem was exposed through commit d80a9cb1a64a ("mm/huge_memory: add and use normal_or_softleaf_folio_pmd()"), it was an oversight in commit af38538801c6 ("mm/memory: factor out common code from vm_normal_page_*()") and would result in other problems: * huge zero folio accounted in smaps, pagemap (PAGE_IS_FILE) and numamaps as file-backed THP * folio_walk_start() returning the folio even without FW_ZEROPAGE set. Callers seem to tolerate that, though.

... and triggering the VM_WARN_ON_ONE(), although never reported so far.

To fix it, teach vm_normal_page_pmd()/vm_normal_page_pud() to consider whether pmd_special/pud_special is actually implemented.

Patch / fix

  • Linux Linux 6.18.34, 7.0.11, 7.1
  • linux Debian 14 7.0.12-1

debian advisories DEBIAN-CVE-2026-64181

  • linux Ubuntu 26.04 LTS 7.0.0-28.28
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1009.9
  • linux-gcp Ubuntu 26.04 LTS 7.0.0-1008.8
  • linux-gke Ubuntu 26.04 LTS 7.0.0-1003.4
  • linux-ibm Ubuntu 26.04 LTS 7.0.0-1010.10
  • linux-azure Ubuntu 26.04 LTS 7.0.0-1010.10
  • linux-raspi Ubuntu 26.04 LTS 7.0.0-1015.15
  • linux-riscv Ubuntu 26.04 LTS 7.0.0-28.28.1

ubuntu advisories UBUNTU-CVE-2026-64181

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-64181 updated cvss 5.5

kernel: mm: fix __vm_normal_page() to handle missing support for pmd_special()/pud_special()

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux 10 kernel
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.17% chance of exploitation in the next 30 days, higher than 6% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Linux Linux

Classification

Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.