# CVE-2026-98135: ntfs: reject invalid sectors_per_cluster in the boot sector

> A local attacker can cause a kernel crash by mounting a crafted NTFS image with an invalid sectors_per_cluster value, leading to an undefined shift operation.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 25 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-98135, GHSA-vhjh-88x6-7w6p, UBUNTU-CVE-2026-98135

## What is CVE-2026-98135?

CVE-2026-98135 is a medium-severity vulnerability in Linux kernel, published on 25 Sep 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:

ntfs: reject invalid sectors_per_cluster in the boot sector

is_boot_sector_ntfs() checks the boot sector's sectors_per_cluster field
with a range test that rejects 0x81..0xf3 but accepts 0 and other
non-power-of-two counts. A zero value reaches parse_ntfs_boot_sector():

	sectors_per_cluster_bits = ffs(sectors_per_cluster) - 1;
	...
	vol->cluster_size = vol->sector_size << sectors_per_cluster_bits;

ffs(0) is 0, so sectors_per_cluster_bits becomes (unsigned)-1 and the
shift is undefined:

  UBSAN: shift-out-of-bounds in fs/ntfs/super.c:673:39
  shift exponent 4294967295 is too large for 32-bit type 'int'

This change rejects any non-power-of-two value, since it feeds the
aforementioned shift via ffs() - 1, which only yields the correct shift for a
power of two.

## Which versions are affected by CVE-2026-98135?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-98135?

Apply the vendor's patch.

## Is CVE-2026-98135 being exploited?

There is no known exploitation of CVE-2026-98135 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-2026-98135 and fix it if it is affected.

What it is: CVE-2026-98135 is a medium-severity vulnerability in Linux kernel, published on 25 Sep 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-2026-98135 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-2026-98135/ (Markdown: https://insights.sbomify.com/CVE-2026-98135/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98135
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98135
- OSV: https://osv.dev/vulnerability/CVE-2026-98135

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98135/
Summaries are generated and may contain mistakes; the official description above is the record.