# CVE-2026-12246: Out of bounds stack write with crafted APL RR

> A crafted APL resource record causes a stack buffer overflow in NSD during zone writing, potentially allowing remote code execution or denial of service.

- **Severity:** High 7.2 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/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:** 25 Jun 2026
- **Updated:** 25 Jun 2026
- **Also known as:** ALPINE-CVE-2026-12246, DEBIAN-CVE-2026-12246, GHSA-xgm5-85mh-3559

## What is CVE-2026-12246?

CVE-2026-12246 is a high-severity memory corruption vulnerability in NLnet Labs NSD, published on 25 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

NSD version 4.14.0 introduced a bug where a specially crafted APL RR, with an adflength larger than permitted for the address family will overwrite the stack when the zone is written to disk, with a maximum of 111 attacker controlled bytes.

Weakness: CWE-20 (Improper Input Validation), CWE-120 (Buffer Copy without Checking Size of Input)

## Which versions are affected by CVE-2026-12246?

It affects 1 product.


Products: Nlnetlabs Nsd.

## How do I fix CVE-2026-12246?

Apply the vendor's patch.

## Is CVE-2026-12246 being exploited?

There is no known exploitation of CVE-2026-12246 in the wild and no public exploit code.

## Other vulnerabilities in NLnet Labs NSD

- [CVE-2026-12244](https://insights.sbomify.com/CVE-2026-12244/): Heap overflow and crash with crafted SVCB RR (high 8.7)
- [CVE-2026-12245](https://insights.sbomify.com/CVE-2026-12245/): Denial of DNS over TLS service by any DoT client (high 8.7)
- [CVE-2026-18664](https://insights.sbomify.com/CVE-2026-18664/): Wrong interpretation of ACL ranges (high 8.2)
- [CVE-2026-19401](https://insights.sbomify.com/CVE-2026-19401/): Remote UDP DoS by sending multiple DNS Cookie options (high 8.2)
- [CVE-2026-19538](https://insights.sbomify.com/CVE-2026-19538/): Bypass of BLOCKED ACL items on proxy protocol port over TCP or TLS (high 8.2)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-12246 and fix it if it is affected.

What it is: CVE-2026-12246 is a high-severity memory corruption vulnerability in NLnet Labs NSD, published on 25 Jun 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-2026-12246 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-2026-12246/ (Markdown: https://insights.sbomify.com/CVE-2026-12246/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-12246
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-12246
- OSV: https://osv.dev/vulnerability/CVE-2026-12246

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-12246/
Summaries are generated and may contain mistakes; the official description above is the record.