# CVE-2026-90200: fs/ntfs3: fix integer overflow in MFT cluster validation

> An integer overflow in the Linux kernel NTFS3 driver allows bypassing validation, leading to mount failures and denial of service when processing malformed boot sectors.

- **Severity:** Not scored
- **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:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-102926, BELL-CVE-2026-90200, DEBIAN-CVE-2026-90200, GHSA-h945-5whj-h8mc, UBUNTU-CVE-2026-90200

## What is CVE-2026-90200?

CVE-2026-90200 is a vulnerability in Linux, published on 17 Sep 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: fix integer overflow in MFT cluster validation

In ntfs_init_from_boot(), the boot sector's MFT cluster numbers are
validated against the volume size with:

	if (mlcn  * sct_per_clst >= sectors ||
	    mlcn2 * sct_per_clst >= sectors)
		goto out;

mlcn and mlcn2 are u64 fields read directly from the boot sector.
sct_per_clst is bounded above by 4096 (true_sectors_per_clst() plus
the is_power_of_2() check below it), but the multiplication is done
in u64 and wraps when mlcn (or mlcn2) is large enough -- e.g. mlcn
near 2^62 with sct_per_clst == 4 wraps to 0, which compares below
any non-zero 'sectors', so the check is bypassed and the malformed
record is accepted.

The accepted mlcn is then used unchanged in

	sbi->mft.lbo = mlcn << cluster_bits;

In practice the resulting reads fail at the block layer (sb_bread()
returns NULL via grow_buffers()'s check_mul_overflow() guard), so
today this manifests as mount failing in odd places rather than as
something more dangerous, but the validation step is still wrong
and there is no reason for callers to rely on the block layer to
catch a value that should never have been accepted in the first
place.

Use check_mul_overflow() to compute the two sector positions and
fail the mount if either multiplication wraps; this preserves the
existing semantics (mlcn * sct_per_clst >= sectors) instead of
switching to division (mlcn >= sectors / sct_per_clst), which
would tighten the check at edge cases where 'sectors' is not a
multiple of sct_per_clst.  The check_*_overflow() style is the
one ntfs3 already uses for similar on-disk arithmetic in
fs/ntfs3/run.c.

## Which versions are affected by CVE-2026-90200?


## How do I fix CVE-2026-90200?

Apply the vendor's patch.

## Is CVE-2026-90200 being exploited?

There is no known exploitation of CVE-2026-90200 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90200 and fix it if it is affected.

What it is: CVE-2026-90200 is a vulnerability in Linux, published on 17 Sep 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-2026-90200 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-2026-90200/ (Markdown: https://insights.sbomify.com/CVE-2026-90200/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90200
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90200
- OSV: https://osv.dev/vulnerability/CVE-2026-90200

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90200/
Summaries are generated and may contain mistakes; the official description above is the record.