# CVE-2026-64533: fs/ntfs3: validate lcns_follow in log_replay conversion

> A malformed NTFS filesystem image can trigger an out-of-bounds memory write in the Linux kernel NTFS3 driver, potentially leading to code execution or system crash.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 27 Jul 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-93962, BELL-CVE-2026-64533, DEBIAN-CVE-2026-64533, GHSA-hvv2-rwwx-6q3h, ROOT-OS-DEBIAN-12-CVE-2026-64533, UBUNTU-CVE-2026-64533

## What is CVE-2026-64533?

CVE-2026-64533 is a high-severity memory corruption vulnerability in Linux, published on 27 Jul 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

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

fs/ntfs3: validate lcns_follow in log_replay conversion

log_replay() converts DIR_PAGE_ENTRY_32 records into DIR_PAGE_ENTRY
records when replaying version 0 restart tables.

During this conversion, the memmove() length is derived directly from
the on-disk lcns_follow field:

	memmove(&dp->vcn, &dp0->vcn_low,
		2 * sizeof(u64) +
				le32_to_cpu(dp->lcns_follow) * sizeof(u64));

check_rstbl() validates restart table structure, but does not constrain
per-entry lcns_follow values relative to the entry size. A malformed
filesystem image can provide an oversized lcns_follow value, causing
the conversion memmove() to access memory beyond the bounds of the
allocated restart table buffer.

The same field is later used to bound iteration over page_lcns[],
so validating lcns_follow during conversion also prevents downstream
out-of-bounds access from the same malformed metadata.

Compute the maximum valid lcns_follow from the already-validated
restart table entry size and reject entries that exceed this bound.
Reuse the existing t16/t32 scratch variables already declared in
log_replay() to avoid introducing new declarations.

[almaz.alexandrovich@paragon-software.com: fixed the conflicts]

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-64533?


## How do I fix CVE-2026-64533?

Apply the vendor's patch.

## Is CVE-2026-64533 being exploited?

There is no known exploitation of CVE-2026-64533 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64533 and fix it if it is affected.

What it is: CVE-2026-64533 is a high-severity memory corruption vulnerability in Linux, published on 27 Jul 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-64533 in the wild and no public exploit code.

Affected product: Linux. 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-2026-64533/ (Markdown: https://insights.sbomify.com/CVE-2026-64533/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64533
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64533
- OSV: https://osv.dev/vulnerability/CVE-2026-64533

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64533/
Summaries are generated and may contain mistakes; the official description above is the record.