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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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
Which versions are affected by CVE-2026-40211?
How do I fix CVE-2026-40211?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-40211 being exploited?
There is no known exploitation of CVE-2026-40211 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-40211, GHSA-8mqg-g8g6-fvw6, UBUNTU-CVE-2026-40211.