CVE-2026-19401

Remote UDP DoS by sending multiple DNS Cookie options

Published Aug 26, 2026 CVSS 4.0 · 8.2 High EPSS < 1% KEV · Not listed
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.

Remediation

Vendor Solution

This issue is fixed in 4.15.1 and all later versions.

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
CPEs cpe:2.3:a:nlnetlabs:nsd:*:*:*:*:*:*:*:*
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Type Values Removed Values Added
First Time appeared Nlnetlabs
Nlnetlabs nsd
Vendors & Products Nlnetlabs
Nlnetlabs nsd
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
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.
Title Remote UDP DoS by sending multiple DNS Cookie options
Weaknesses CWE-400
CWE-617
References
Metrics cvssV4_0

{'score': 8.2, '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'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
NLnet Labs
Published
Updated
Aug 26, 2026, 2:16 PM
Reserved
Aug 10, 2026, 7:31 AM
Status
Analyzed
Published
Aug 26, 2026, 9:16 AM
Modified
Sep 8, 2026, 8:00 PM