# CVE-2026-90096: fuse: invalidate the correct range after O_APPEND direct write

> A race condition in the Linux kernel FUSE module allows local attackers to read stale data from file tails during concurrent direct and buffered writes.

- **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:** GHSA-279q-p928-6329, UBUNTU-CVE-2026-90096

## What is CVE-2026-90096?

CVE-2026-90096 is a 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:

fuse: invalidate the correct range after O_APPEND direct write

fuse_direct_write_iter() captures pos before generic_write_checks(),
which moves ki_pos to EOF for O_APPEND writes:

  fuse_direct_write_iter()
  {
      pos = iocb->ki_pos;           /* 0 (user-supplied)       */
      generic_write_checks();       /* ki_pos -> EOF           */
      fuse_direct_io();             /* writes at EOF, correct  */
      invalidate(pos, pos + res);   /* [0, res) -- wrong       */
  }

The post-write invalidation targets a stale range instead of the
actual written range at EOF.

This can cause data inconsistency when the file size is not
page-aligned.  The tail page straddling EOF has a valid portion
before EOF that concurrent readers can fault back in during the
DIO write window:

  Tail page (file size X not page-aligned):

    page_start         X (EOF)   page_end
    |--- valid data ----|-- stale --|

  CPU0 (O_APPEND DIO writer)    CPU1 (buffered reader)
  --------------------------    ----------------------
  invalidate [X, X+len)
    tail page evicted
  FUSE_WRITE in flight ...
                                read [page_start, X)
                                  tail page re-faulted
                                  [X, page_end) = stale
  FUSE_WRITE completes
  i_size = X + len
  invalidate [0, len)  <- WRONG
    tail page still cached
                                read [X, X+len)
                                  hits stale tail page
                                  returns old data

Fix by reading pos back from iocb->ki_pos after generic_write_checks(),
as generic_file_direct_write() does.

Also fix a typo in the comment ("may have" -> "may have competed").

## Which versions are affected by CVE-2026-90096?


## How do I fix CVE-2026-90096?

Apply the vendor's patch.

## Is CVE-2026-90096 being exploited?

There is no known exploitation of CVE-2026-90096 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90096 and fix it if it is affected.

What it is: CVE-2026-90096 is a 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-2026-90096 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-2026-90096/ (Markdown: https://insights.sbomify.com/CVE-2026-90096/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90096
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90096
- OSV: https://osv.dev/vulnerability/CVE-2026-90096

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90096/
Summaries are generated and may contain mistakes; the official description above is the record.