# CVE-2026-33259: Concurrent modification of RPZ data can lead to denial of servce

> Concurrent RPZ transfers can cause use-after-free and crashes in PowerDNS Recursor, leading to denial of service.

- **Severity:** Medium 5.0 (`CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Apr 2026
- **Updated:** 22 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-33259, GHSA-6c6h-9v3q-3wqm, UBUNTU-CVE-2026-33259

## What is CVE-2026-33259?

CVE-2026-33259 is a medium-severity use after free vulnerability in Powerdns Recursor, published on 22 Apr 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

Having many concurrent transfers of the same RPZ can lead to inconsistent RPZ data, use after free and/or a crash of the recursor. Normally concurrent transfers of the same RPZ zone can only occur with a malfunctioning RPZ provider.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-33259?

It affects 1 product.


Products: Powerdns Recursor.

## How do I fix CVE-2026-33259?

Apply the vendor's patch.

## Is CVE-2026-33259 being exploited?

There is no known exploitation of CVE-2026-33259 in the wild and no public exploit code.

## Other vulnerabilities in Powerdns Recursor

- [CVE-2009-4009](https://insights.sbomify.com/CVE-2009-4009/): Memory corruption in n/a (critical 10.0)
- [CVE-2020-10030](https://insights.sbomify.com/CVE-2020-10030/): Memory corruption in n/a (high 8.8)
- [CVE-2025-59023](https://insights.sbomify.com/CVE-2025-59023/): Crafted delegations or IP fragments can poison cached delegations in Recursor (high 8.2)
- [CVE-2025-59030](https://insights.sbomify.com/CVE-2025-59030/): Insufficient validation of incoming notifies over TCP can lead to a denial of service in Recursor (high 7.5)
- [CVE-2023-22617](https://insights.sbomify.com/CVE-2023-22617/): Denial of service in n/a (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-33259 and fix it if it is affected.

What it is: CVE-2026-33259 is a medium-severity use after free vulnerability in Powerdns Recursor, published on 22 Apr 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-33259 in the wild and no public exploit code.

Affected product: Powerdns Recursor. 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-2026-33259/ (Markdown: https://insights.sbomify.com/CVE-2026-33259/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33259
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33259
- OSV: https://osv.dev/vulnerability/CVE-2026-33259

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-33259/
Summaries are generated and may contain mistakes; the official description above is the record.