CVE-2026-40209 Denial of service via IXFR queries
Attackers can cause denial of service in PowerDNS DNSdist by sending IXFR queries that exhaust backend connections or file descriptors.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-40209?
CVE-2026-40209 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 might be able to cause outgoing TCP connections to backend to be stuck until a timeout occurs instead of being released immediately, by sending IXFR queries. This could be used to cause a denial of service if there is a limit to the number of concurrent connections to this backend, or if the process runs out of file descriptors.
Weakness: CWE-772
Which versions are affected by CVE-2026-40209?
How do I fix CVE-2026-40209?
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-2026-40209 being exploited?
There is no known exploitation of CVE-2026-40209 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-40209, GHSA-c5m7-ppm5-wp5g, UBUNTU-CVE-2026-40209.