# CVE-2026-12244: Heap overflow and crash with crafted SVCB RR

> A secondary NSD server can be crashed or subjected to remote code execution by a malicious primary zone via a crafted SVCB record causing an integer overflow.

- **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:** 25 Jun 2026
- **Updated:** 25 Jun 2026
- **Also known as:** ALPINE-CVE-2026-12244, DEBIAN-CVE-2026-12244, GHSA-p22w-wq6p-g85g

## What is CVE-2026-12244?

CVE-2026-12244 is a high-severity 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

If NSD is configured as secondary for a zone, the primary of that zone can crash NSD with an AXFR containing a DNS message with a special crafted SVCB RR with an rdata size of 65512, that let's an (uint16_t) variable that is used to allocate space needed for the RR wrap (because total size > 65535), causing a heap overflow. The attacker can perform a controlled (RCE class) head write of up to 65509 bytes

Weakness: CWE-190 (Integer Overflow or Wraparound), CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2026-12244?

It affects 1 product.


Products: Nlnetlabs Nsd.

## How do I fix CVE-2026-12244?

Apply the vendor's patch.

## Is CVE-2026-12244 being exploited?

There is no known exploitation of CVE-2026-12244 in the wild and no public exploit code.

## Other vulnerabilities in NLnet Labs NSD

- [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)
- [CVE-2026-12490](https://insights.sbomify.com/CVE-2026-12490/): Bypass of client certificate verification with transfer over TLS (high 8.2)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-12244 and fix it if it is affected.

What it is: CVE-2026-12244 is a high-severity 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-2026-12244 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-2026-12244/ (Markdown: https://insights.sbomify.com/CVE-2026-12244/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-12244
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-12244
- OSV: https://osv.dev/vulnerability/CVE-2026-12244

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-12244/
Summaries are generated and may contain mistakes; the official description above is the record.