# CVE-2026-98684: smb: client: flush and commit data before querying allocated ranges


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-110462, BELL-CVE-2026-98684, DEBIAN-CVE-2026-98684, GHSA-6247-f99h-hr72, UBUNTU-CVE-2026-98684

## What is CVE-2026-98684?

CVE-2026-98684 is a vulnerability in Linux, published on 18 Oct 2026. 

### Official description

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

smb: client: flush and commit data before querying allocated ranges

The mode 0 / FALLOC_FL_KEEP_SIZE fallocate emulation for small interior
ranges in smb3_simple_fallocate_range() issues
FSCTL_QUERY_ALLOCATED_RANGES and zero-fills any sub-range the server
reports as an unallocated hole, to force block allocation without
changing file contents.

This is unsafe against Windows servers.  Per the Win32 documentation,
FSCTL_QUERY_ALLOCATED_RANGES only reports ranges that *may* contain
nonzero data and is explicitly not coherent with recently written data:

  "a call to FSCTL_QUERY_ALLOCATED_RANGES [after writing to a network
   file] would not necessarily return a correct list of allocated
   regions.  To ensure coherency [...] flush the data to the file"

fsx (generic/363) reproduces the resulting corruption against Windows
Server 2022: a range is written, an uncached read returns the data, yet
the next FSCTL_QUERY_ALLOCATED_RANGES on that range reports it as a whole
hole, so the emulation overwrites live data with zeroes.  A network trace
confirmed the WRITE, the READ returning data and the query returning an
empty range list within microseconds.  Samba does not exhibit this; its
query is coherent with the written data.

Write back the dirty pages, drain any outstanding I/O and issue an SMB2
FLUSH to force the server to commit the data before querying the
allocated ranges, so the query reflects the data actually present.

With this, generic/363 passes against both Windows Server 2022 and Samba
over 100000 fsx operations.

## Which versions are affected by CVE-2026-98684?


## How do I fix CVE-2026-98684?

Upgrade to a fixed version.

## Is CVE-2026-98684 being exploited?

There is no known exploitation of CVE-2026-98684 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98684 and fix it if it is affected.

What it is: CVE-2026-98684 is a vulnerability in Linux, published on 18 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-98684 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-2026-98684/ (Markdown: https://insights.sbomify.com/CVE-2026-98684/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98684
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98684
- OSV: https://osv.dev/vulnerability/CVE-2026-98684

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98684/
Summaries are generated and may contain mistakes; the official description above is the record.