# CVE-2026-99083: ksmbd: fix heap out-of-bounds write in krb5_authenticate()


- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 26 Oct 2026
- **Also known as:** AZL-110990, BELL-CVE-2026-99083, DEBIAN-CVE-2026-99083, GHSA-2j87-48p3-j5xw, UBUNTU-CVE-2026-99083

## What is CVE-2026-99083?

CVE-2026-99083 is a high-severity vulnerability in Linux, published on 23 Oct 2026. 

### Official description

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

ksmbd: fix heap out-of-bounds write in krb5_authenticate()

In krb5_authenticate(), out_len is calculated to determine available
headroom in response_buf for the incoming Kerberos AP-REP token. However,
when SMB2_SESSION_SETUP is processed as a non-first element of a compounded
SMB2 request, the calculation omits work->next_smb2_rsp_hdr_off.

This causes out_len to overstate remaining buffer headroom by
the cumulative size of prior responses in the compound chain. Consequently,
the length check in ksmbd_krb5_authenticate()
(*out_len <= resp->spnego_blob_len) passes erroneously, allowing memcpy()
to write the AP-REP blob past the end of response_buf into adjacent kernel
heap memory.

Fix this by subtracting work->next_smb2_rsp_hdr_off when computing out_len,
ensuring it accurately reflects physical remaining buffer space.

## Which versions are affected by CVE-2026-99083?


## How do I fix CVE-2026-99083?

Upgrade to a fixed version.

## Is CVE-2026-99083 being exploited?

There is no known exploitation of CVE-2026-99083 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99083 and fix it if it is affected.

What it is: CVE-2026-99083 is a high-severity vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99083 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-2026-99083/ (Markdown: https://insights.sbomify.com/CVE-2026-99083/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99083
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99083
- OSV: https://osv.dev/vulnerability/CVE-2026-99083

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99083/
Summaries are generated and may contain mistakes; the official description above is the record.