# CVE-2026-44608: Use after free and crash under special conditions in RPZ code

> Attackers can cause a crash in Unbound DNS resolver via use-after-free during RPZ zone transfers in multi-threaded environments.

- **Severity:** Medium 4.6 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Amber`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 May 2026
- **Updated:** 20 May 2026
- **Also known as:** ALPINE-CVE-2026-44608, AZL-87024, DEBIAN-CVE-2026-44608, ECHO-28d0-99d8-d11d, GHSA-fx8q-9cm5-75v9, UBUNTU-CVE-2026-44608

## What is CVE-2026-44608?

CVE-2026-44608 is a medium-severity use after free vulnerability in Nlnetlabs Unbound, published on 20 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a locking inconsistency vulnerability that when certain conditions are met (multi-threaded, RPZ XFR reload, RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers) it could result in heap use-after-free and eventual crash. An adversary can exploit the vulnerability if conditions are first met on a vulnerable Unbound, i.e., multi-threaded, an RPZ zone with 'rpz-nsip'/'rpz-nsdname' triggers and an ongoing XFR for that RPZ zone. Local RPZ files do not trigger the vulnerability. If the timing is right and an XFR happens at the same time another thread needs to read that RPZ zone, the reader may not hold the lock long enough and the thread applying the XFR may free objects that the reader is about to walk causing the use-after-free. Unbound 1.25.1 contains a patch with a fix to the locking code.

Weakness: CWE-413 (Improper Resource Locking)

## Which versions are affected by CVE-2026-44608?

It affects 1 product.


Products: Nlnetlabs Unbound.

## How do I fix CVE-2026-44608?

Apply the vendor's patch.

## Is CVE-2026-44608 being exploited?

There is no known exploitation of CVE-2026-44608 in the wild and no public exploit code.

## Other vulnerabilities in Nlnetlabs Unbound

- [CVE-2026-81642](https://insights.sbomify.com/CVE-2026-81642/): Heap buffer overflow and possible Remote Code Execution when digesting DNSKEY (critical 9.1)
- [CVE-2026-33278](https://insights.sbomify.com/CVE-2026-33278/): Possible arbitrary code execution during DNSSEC validation (critical 9.1)
- [CVE-2026-42944](https://insights.sbomify.com/CVE-2026-42944/): Heap overflow with multiple NSID, COOKIE, PADDING EDNS options (high 8.7)
- [CVE-2026-42959](https://insights.sbomify.com/CVE-2026-42959/): Crash during DNSSEC validation of malicious content (high 8.7)
- [CVE-2026-82717](https://insights.sbomify.com/CVE-2026-82717/): CNAME synthesis could lead to heap corruption (high 8.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-44608 and fix it if it is affected.

What it is: CVE-2026-44608 is a medium-severity use after free vulnerability in Nlnetlabs Unbound, published on 20 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-44608 in the wild and no public exploit code.

Affected product: Nlnetlabs Unbound. 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-2026-44608/ (Markdown: https://insights.sbomify.com/CVE-2026-44608/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-44608
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-44608
- OSV: https://osv.dev/vulnerability/CVE-2026-44608

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-44608/
Summaries are generated and may contain mistakes; the official description above is the record.