CVE-2026-19401
Received Received - Intake

NSD DNS Cookie Options Remote Crash Vulnerability

Publication date: 2026-08-26

Last updated on: 2026-08-26

Assigner: NLnet Labs

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.

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Meta Information

Published
2026-08-26
Last Modified
2026-08-26
Generated
2026-08-26
AI Q&A
2026-08-26
EPSS Evaluated
N/A
NVD
CVE-2026-19401
EUVD
EUVD-2026-66349

Affected Vendors & Products

Currently, no data is known.

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-400 The product does not properly control the allocation and maintenance of a limited resource.
CWE-617 The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.

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Executive Summary

This vulnerability allows a remote attacker to crash the NSD DNS server by sending a specially crafted message with 17 DNS Cookie options when the UDP payload size is 512. Repeated crashes can degrade or completely disrupt DNS service for users.

Detection Guidance

Detecting this vulnerability requires monitoring for crashes in NSD server child processes triggered by malformed DNS Cookie options. Check logs for repeated crashes of nsd child processes and inspect incoming DNS traffic for packets with 17 Cookie options in UDP payloads of 512 bytes.

Impact Analysis

If exploited, this could lead to DNS service outages, making it difficult for users to access websites or services that rely on DNS resolution. In severe cases, it may cause a complete denial of DNS service.

Mitigation Strategies

Upgrade NSD to a patched version that handles DNS Cookie options safely. If upgrading is not immediate, restrict access to NSD servers via firewalls or network segmentation to reduce exposure. Monitor for unusual traffic patterns targeting DNS ports.

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