# CVE-2026-101337: Stack overwrite from specially formatted base64 RDATA field

> Attackers can overwrite the stack via specially formatted base64 RDATA fields in zone files, potentially leading to code execution.

- **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-2026-101337, DEBIAN-CVE-2026-101337, GHSA-w2rq-89vw-p64m, UBUNTU-CVE-2026-101337

## What is CVE-2026-101337?

CVE-2026-101337 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 base64 data is split up in pieces, of 3 character or less, tokens were incorrectly calculated to produce 0 bytes. This enables attackers to overwrite the stack with up to 64K of attacker controlled data.  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-2026-101337?


## How do I fix CVE-2026-101337?

Apply the vendor's patch.

## Is CVE-2026-101337 being exploited?

There is no known exploitation of CVE-2026-101337 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-101337 and fix it if it is affected.

What it is: CVE-2026-101337 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-2026-101337 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-2026-101337/ (Markdown: https://insights.sbomify.com/CVE-2026-101337/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-101337
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-101337
- OSV: https://osv.dev/vulnerability/CVE-2026-101337

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-101337/
Summaries are generated and may contain mistakes; the official description above is the record.