---
title: "CVE-2026-40211\n    | Ubuntu"
description: Ubuntu is an open source software operating system that runs from the
  desktop, to the cloud, to all your internet connected things.
url: https://ubuntu.com/security/CVE-2026-40211?format=md
keywords: index, follow
---

# CVE-2026-40211

Publication date 25 June 2026

Last updated 29 June 2026

---

Ubuntu priority

**Medium**

[Why this priority?](https://ubuntu.com/security/cves/about#priority )

## Cvss 3 Severity Score

**5.3 · Medium**

[Score breakdown](https://ubuntu.com/security/CVE-2026-40211?format=md#impact-score)

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## 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.

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| dnsdist | 26.04 LTS resolute | Needs evaluation |
| 25.10 questing | Ignored end of life, was needs-triage |
| 24.04 LTS noble | Needs evaluation |
| 22.04 LTS jammy | Needs evaluation |
| 20.04 LTS focal | Needs evaluation |
| 18.04 LTS bionic | Needs evaluation |
| 16.04 LTS xenial | Needs evaluation |

---

* [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)
* [What do statuses mean?](https://ubuntu.com/security/cves/about#statuses)

## Severity score breakdown

CVSS version:
CVSS v3.0

**Base score**

5.3 · Medium

* Base metrics

  | Parameter | Value |
  | --- | --- |
  | Attack vector | Network |
  | Attack complexity | Low |
  | Privileges required | None |
  | User interaction | None |
  | Scope | Unchanged |
  | Confidentiality impact | None |
  | Integrity impact | None |
  | Availability impact | Low |
* Scores

  | Parameter | Value |
  | --- | --- |
  | Base score | 5.3 · Medium |
  | Exploitability score | - |
  | Impact score | - |

**Vector:** CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-40211)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2026-40211)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2026-40211)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2026-40211)

### Other references

* <https://www.cve.org/CVERecord?id=CVE-2026-40211>
* <https://www.dnsdist.org/security-advisories/powerdns-advisory-for-dnsdist-2026-09.html#cve-2026-40211-denial-of-service-via-crafted-doh3-queries>