# CVE-2026-68431: ksmbd: validate minimum PDU size for transform requests

> An unauthenticated attacker can read memory beyond the request allocation by sending a short SMB2 transform packet to the ksmbd kernel module.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 12 Aug 2026
- **Updated:** 23 Aug 2026
- **Also known as:** BELL-CVE-2026-68431, DEBIAN-CVE-2026-68431, GHSA-6pm5-g7cv-g948, UBUNTU-CVE-2026-68431

## What is CVE-2026-68431?

CVE-2026-68431 is a critical vulnerability in Linux, published on 12 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

ksmbd: validate minimum PDU size for transform requests

The receive path applies the minimum SMB2 PDU size check only when
ProtocolId is SMB2_PROTO_NUMBER. A packet carrying
SMB2_TRANSFORM_PROTO_NUM bypasses the check even when the negotiated
dialect does not provide transform handling.

On an SMB 2.1 connection, a short transform packet therefore reaches
init_smb2_rsp_hdr(), which interprets the request as a full SMB2 header
and reads beyond the request allocation. The copied fields can then be
returned to the unauthenticated client.

Compression transforms are converted to ordinary SMB2 messages before
protocol validation. After that conversion, validate ordinary SMB2
requests against SMB2_MIN_SUPPORTED_PDU_SIZE and require encryption
transform requests to contain both a transform header and an SMB2
header. This rejects truncated requests before work allocation.

## Which versions are affected by CVE-2026-68431?


## How do I fix CVE-2026-68431?

Apply the vendor's patch.

## Is CVE-2026-68431 being exploited?

There is no known exploitation of CVE-2026-68431 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-68431 and fix it if it is affected.

What it is: CVE-2026-68431 is a critical vulnerability in Linux, published on 12 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-68431 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-2026-68431/ (Markdown: https://insights.sbomify.com/CVE-2026-68431/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-68431
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-68431
- OSV: https://osv.dev/vulnerability/CVE-2026-68431

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-68431/
Summaries are generated and may contain mistakes; the official description above is the record.