# CVE-2026-40211: Denial of service via crafted DoH3 queries

> An attacker can cause a denial of service in PowerDNS DNSdist by sending crafted DNS over HTTP/3 queries that trigger an out-of-memory condition.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Jun 2026
- **Updated:** 25 Jun 2026
- **Also known as:** DEBIAN-CVE-2026-40211, GHSA-8mqg-g8g6-fvw6, UBUNTU-CVE-2026-40211

## What is CVE-2026-40211?

CVE-2026-40211 is a medium-severity denial of service vulnerability in PowerDNS DNSdist, published on 25 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An attacker can send crafted DNS over HTTP/3 queries, triggering an exception that prevents some buffer from being freed right away. The buffer will be freed at the end of the QUIC connection, but on some setups it might be possible to open enough concurrent DoH3 streams to trigger an out-of-memory condition, resulting in a denial of service.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2026-40211?


## How do I fix CVE-2026-40211?

Apply the vendor's patch.

## Is CVE-2026-40211 being exploited?

There is no known exploitation of CVE-2026-40211 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40211 and fix it if it is affected.

What it is: CVE-2026-40211 is a medium-severity denial of service vulnerability in PowerDNS DNSdist, published on 25 Jun 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-2026-40211 in the wild and no public exploit code.

Affected product: PowerDNS DNSdist. 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-2026-40211/ (Markdown: https://insights.sbomify.com/CVE-2026-40211/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40211
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40211
- OSV: https://osv.dev/vulnerability/CVE-2026-40211

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40211/
Summaries are generated and may contain mistakes; the official description above is the record.