CVE-2026-40209

Name	CVE-2026-40209
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.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
References	DSA-6367-1

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
dnsdist (PTS)	bullseye	1.5.1-3	vulnerable
	bookworm	1.7.3-2	vulnerable
	trixie (security), trixie	1.9.15-0+deb13u1	fixed
	forky, sid	2.1.0-2	fixed

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin
dnsdist	source	bullseye	(unfixed)	end-of-life
dnsdist	source	bookworm	(unfixed)	end-of-life
dnsdist	source	trixie	1.9.15-0+deb13u1		DSA-6367-1
dnsdist	source	(unstable)	2.1.0-1

Notes

[bookworm] - dnsdist <end-of-life> (See #1119290)
[bullseye] - dnsdist <end-of-life> (see #1119290)
https://www.dnsdist.org/security-advisories/powerdns-advisory-for-dnsdist-2026-09.html#cve-2026-40209-denial-of-service-via-ixfr-queries