# CVE-2026-90117: ntfs: validate usa_ofs before preserving the update sequence number

> A use-after-free vulnerability in the Linux kernel NTFS driver allows local attackers to cause a system crash or potentially execute code via a crafted filesystem image.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-90117, GHSA-v5jv-j5cw-ggjq, UBUNTU-CVE-2026-90117

## What is CVE-2026-90117?

CVE-2026-90117 is an use after free vulnerability in Linux, published on 17 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: validate usa_ofs before preserving the update sequence number

When ntfs_mft_record_alloc() reuses a free mft record it reads the old
update sequence number straight from the on-disk record:

     usn = *(__le16 *)((u8 *)m + le16_to_cpu(m->usa_ofs));

Here m points into the raw $MFT page-cache folio, which still holds
unvalidated, MST-protected bytes: the folio is read by a plain
iomap_read_folio() and neither post_read_mst_fixup() nor
ntfs_mft_record_check() has run on it (both work on private copies).
m->usa_ofs is therefore an untrusted u16, and a corrupted record can put
it past the end of the record so the two-byte read lands outside the
folio.  Reading such a record while creating a file gives, under KASAN:

   BUG: KASAN: use-after-free in ntfs_mft_record_alloc+...
   Read of size 2 at addr ...
    ntfs_mft_record_alloc -> __ntfs_create -> ntfs_create -> path_openat

Only preserve the old update sequence number when usa_ofs is even and in
range, mirroring the check ntfs_mft_record_check() already applies;
otherwise leave usn zero, which the existing restore below skips.

## Which versions are affected by CVE-2026-90117?


## How do I fix CVE-2026-90117?

Apply the vendor's patch.

## Is CVE-2026-90117 being exploited?

There is no known exploitation of CVE-2026-90117 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90117 and fix it if it is affected.

What it is: CVE-2026-90117 is an use after free vulnerability in Linux, published on 17 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-2026-90117 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-2026-90117/ (Markdown: https://insights.sbomify.com/CVE-2026-90117/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90117
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90117
- OSV: https://osv.dev/vulnerability/CVE-2026-90117

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90117/
Summaries are generated and may contain mistakes; the official description above is the record.