CVE-2026-19401
Remote UDP DoS by sending multiple DNS Cookie options
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.
INFO
Published Date :
Aug. 26, 2026, 8:44 a.m.
Last Modified :
Aug. 26, 2026, 8:44 a.m.
Remotely Exploit :
No
Source :
NLnet Labs
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 4.0 | HIGH | 206fc3a0-e175-490b-9eaa-a5738056c9f6 |
Solution
- Use release builds instead of debugging builds.
- Validate DNS Cookie option counts.
- Implement robust message parsing.
- Update NSD server software.
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CVE-2026-19401 vulnerability anywhere in the article.