Vulnerability · Published Aug 26, 2026 · Assigned by NLnet Labs

CVE-2026-19401Remote UDP DoS by sending multiple DNS Cookie options

High 8.2

In plain English

A high-severity uncontrolled resource consumption in NSD from NLnet Labs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 40% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)8.2High

Exploit odds (30 days)0.5%top 60.0% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Any remote client can crash a (debugging/non-release build type) NSD serve child by sending it a special crafted message with a specially tuned number of DNS Cookie options (17 when UDP payload size is 512). By continuously crashing the serve childs, the remote client can severely hamper or, when positioned sufficiently close, deny all DNS service.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	nsd	no fix listed	DEBIAN-CVE-2026-19401
Debian:13	nsd	no fix listed	DEBIAN-CVE-2026-19401
Debian:14	nsd	4.15.1-1	DEBIAN-CVE-2026-19401
Ubuntu:26.10	nsd	no fix listed	UBUNTU-CVE-2026-19401

Affected products (as reported)

Vendor	Product	Versions
NLnet Labs	NSD	4.3.7 – before 4.15.1

Weakness: CWE-617, CWE-400 · Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

References

https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-19401.txt vendor-advisory