# CVE-2026-64181: mm: fix __vm_normal_page() to handle missing support for pmd_special()/pud_special()

> A kernel bug in memory management on 32-bit x86 systems with THP enabled can cause system crashes and memory accounting errors.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jul 2026
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2026-64181, DEBIAN-CVE-2026-64181, GHSA-jx9m-72fr-5v84, UBUNTU-CVE-2026-64181

## What is CVE-2026-64181?

CVE-2026-64181 is a high-severity vulnerability in Linux kernel, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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.

## Which versions are affected by CVE-2026-64181?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-64181?

Apply the vendor's patch.

## Is CVE-2026-64181 being exploited?

There is no known exploitation of CVE-2026-64181 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64181 and fix it if it is affected.

What it is: CVE-2026-64181 is a high-severity vulnerability in Linux kernel, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-64181 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-64181/ (Markdown: https://insights.sbomify.com/CVE-2026-64181/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64181
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64181
- OSV: https://osv.dev/vulnerability/CVE-2026-64181

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64181/
Summaries are generated and may contain mistakes; the official description above is the record.