# CVE-2026-101338: Stack overwrite from a specially crafted and formatted SVCB or HTTPS RR

> A stack overwrite in NSD allows attackers to execute arbitrary code or cause denial of service via crafted SVCB or HTTPS resource records.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 14 Oct 2026
- **Updated:** 14 Oct 2026
- **Also known as:** ALPINE-CVE-2026-101338, DEBIAN-CVE-2026-101338, GHSA-r5wh-92fx-cv6j, UBUNTU-CVE-2026-101338

## What is CVE-2026-101338?

CVE-2026-101338 is a high-severity memory corruption vulnerability in NLnet Labs NSD, published on 14 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

When a SVCB or HTTPS RR has filled the wire format RDATA up to the brim, another ECH parameter may overwrite the stack, and once beyond the limit, the base64 decoder can write attacker controlled data of unlimited size.  Zone files which are written out by NSD itself, such as for zones for which the NSD instance is secondary, will not be formatted like this. The zone file must be fed to NSD directly, (but it could come, for example, from an operator controlled provisioning system).

Weakness: CWE-121 (Stack-based Buffer Overflow)

## Which versions are affected by CVE-2026-101338?


## How do I fix CVE-2026-101338?

Apply the vendor's patch.

## Is CVE-2026-101338 being exploited?

There is no known exploitation of CVE-2026-101338 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-101338 and fix it if it is affected.

What it is: CVE-2026-101338 is a high-severity memory corruption vulnerability in NLnet Labs NSD, published on 14 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-101338 in the wild and no public exploit code.

Affected product: NLnet Labs NSD. 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-2026-101338/ (Markdown: https://insights.sbomify.com/CVE-2026-101338/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-101338
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-101338
- OSV: https://osv.dev/vulnerability/CVE-2026-101338

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-101338/
Summaries are generated and may contain mistakes; the official description above is the record.