# CVE-2026-98171: smb: client: fix next_buffer UAF and NextCommand bounds in compound PDUs

> A use-after-free and bounds checking flaw in the Linux kernel SMB client allows attackers to execute code or cause denial of service via crafted compound PDUs.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 6 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-106215, BELL-CVE-2026-98171, DEBIAN-CVE-2026-98171, GHSA-68gh-wq6f-89rf, UBUNTU-CVE-2026-98171

## What is CVE-2026-98171?

CVE-2026-98171 is a high-severity use after free vulnerability in Linux, published on 6 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

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

smb: client: fix next_buffer UAF and NextCommand bounds in compound PDUs

Fix several related bounds checking and pointer lifecycle issues in
receive_encrypted_standard()'s handling of compound encrypted frames:

- Clear next_buffer after assigning it to server->bigbuf. A stale
  next_buffer pointer can lead to a use-after-free on subsequent
  error paths.
- Update pdu_length to the decrypted plaintext size (buf_size). Using
  the pre-decryption length allows NextCommand to point into stale
  ciphertext residue.
- Reject next_cmd values smaller than MID_HEADER_SIZE(server).
- Fix an integer overflow in the upper bound check by verifying
  pdu_length - next_cmd < MID_HEADER_SIZE(server), ensuring the
  trailing slice is large enough for a header.

## Which versions are affected by CVE-2026-98171?


## How do I fix CVE-2026-98171?

Apply the vendor's patch.

## Is CVE-2026-98171 being exploited?

There is no known exploitation of CVE-2026-98171 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98171 and fix it if it is affected.

What it is: CVE-2026-98171 is a high-severity use after free vulnerability in Linux, published on 6 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-98171 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-2026-98171/ (Markdown: https://insights.sbomify.com/CVE-2026-98171/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98171
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98171
- OSV: https://osv.dev/vulnerability/CVE-2026-98171

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98171/
Summaries are generated and may contain mistakes; the official description above is the record.