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, 9:16 a.m.
Last Modified :
Sept. 8, 2026, 8 p.m.
Remotely Exploit :
No
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | [email protected] | ||||
| CVSS 4.0 | HIGH | 206fc3a0-e175-490b-9eaa-a5738056c9f6 | ||||
| CVSS 4.0 | HIGH | [email protected] |
Solution
- Use release builds instead of debugging builds.
- Validate DNS Cookie option counts.
- Implement robust message parsing.
- Update NSD server software.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-19401.
| URL | Resource |
|---|---|
| https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-19401.txt | Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-19401 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-19401
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-19401 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-19401 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Sep. 08, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Added CPE Configuration OR *cpe:2.3:a:nlnetlabs:nsd:*:*:*:*:*:*:*:* versions from (including) 4.3.7 up to (excluding) 4.15.1 Added Reference Type NLnet Labs: https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-19401.txt Types: Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Aug. 26, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-19401', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-08-26T14:09:46.662987Z'} -
New CVE Received by [email protected]
Aug. 26, 2026
Action Type Old Value New Value 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. Added CVSS V4.0 AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CWE CWE-400 Added CWE CWE-617 Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/19xxx/CVE-2026-19401.json">CVE-2026-19401</a> Added Reference https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-19401.txt