# CVE-2026-93794: smb/client: flush dirty data before punching a hole

> A flaw in the Linux kernel SMB client allows attackers to read stale data from punched holes due to improper cache flushing.

- **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:** 24 Sep 2026
- **Updated:** 3 Oct 2026
- **Also known as:** AZL-103667, BELL-CVE-2026-93794, DEBIAN-CVE-2026-93794, GHSA-5fcw-5g57-rhgg, UBUNTU-CVE-2026-93794

## What is CVE-2026-93794?

CVE-2026-93794 is a vulnerability in Linux, published on 24 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:

smb/client: flush dirty data before punching a hole

Punching a hole after a large buffered write may leave the range
reported as data. Reproduce it with:

  xfs_io -f \
    -c "pwrite -b 3m -S 0x61 0 3m" \
    -c "fpunch 1m 1m" \
    -c "seek -h 0" \
    -c "seek -d 1m" \
    /mnt/test/repro

Punching 1 MiB at offset 1 MiB should produce:

  0          1 MiB       2 MiB       3 MiB
  |  DATA    |   HOLE    |   DATA    | EOF

Instead, the entire file is reported as data. SEEK_HOLE(0) returns EOF,
and SEEK_DATA(1M) returns 1M.

This happens because a dirty folio spanning the punched range can be
written back after the punch and refill the hole.

Fix this by flushing and waiting for dirty data in the punched range
before invalidating the page cache and issuing FSCTL_SET_ZERO_DATA.

The xfstests generic/539 pass against Samba/ksmbd with this change.

## Which versions are affected by CVE-2026-93794?


## How do I fix CVE-2026-93794?

Apply the vendor's patch.

## Is CVE-2026-93794 being exploited?

There is no known exploitation of CVE-2026-93794 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93794 and fix it if it is affected.

What it is: CVE-2026-93794 is a vulnerability in Linux, published on 24 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-2026-93794 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-2026-93794/ (Markdown: https://insights.sbomify.com/CVE-2026-93794/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93794
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93794
- OSV: https://osv.dev/vulnerability/CVE-2026-93794

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-93794/
Summaries are generated and may contain mistakes; the official description above is the record.