CVE-2026-19401: high-severity vulnerability in NLnet Labs NSD
Remote UDP DoS by sending multiple DNS Cookie options
Published
E-mail alert when it lands in KEV, gets a public PoC or its score goes up.
21Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 8.2epss 0.5%
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.
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
Affected products
NLnet Labs · NSDRelated CVEs — NLnet Labs NSD
In the same product, most dangerous first.
CVE-2020-28935—Local symlink attack in Unbound and NSDEPSS 0.5%CVE-2026-12244HIGHHeap overflow and crash with crafted SVCB RREPSS 0.5%CVE-2026-18916MEDIUMRemote TCP DoS by throttling the TCP receive windowEPSS 0.5%CVE-2026-12245HIGHDenial of DNS over TLS service by any DoT clientEPSS 0.5%CVE-2026-12246HIGHOut of bounds stack write with crafted APL RREPSS 0.4%CVE-2026-19538HIGHBypass of BLOCKED ACL items on proxy protocol port over TCP or TLSEPSS 0.4%