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CVE-2026-19401— Remote UDP DoS by sending multiple DNS Cookie options

Quick assessment

Affected
NLnet Labs NSD
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

NLnet Labs NSD是荷兰NLnet Labs组织的一款DNS服务器软件。 NLnet Labs NSD 4.3.7至4.15.1之前版本存在安全漏洞，该漏洞源于调试/非发布构建类型的NSD服务对特制的DNS Cookie选项消息处理不当，可能使远程客户端导致服务子进程崩溃，持续攻击可造成拒绝服务。

CVSS 8.2 · High EPSS 0.28% · P19

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 1

VendorProduct Version RangeStatus
NLnet Labs NSD 4.3.7< 4.15.1 affected
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I. Basic Information for CVE-2026-19401

Vulnerability Information
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Vulnerability Title
Remote UDP DoS by sending multiple DNS Cookie options
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
可达断言
Source: CVE Program / CVE List V5
Vulnerability Title
NLnet Labs NSD 异常处理不当漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
NLnet Labs NSD是荷兰NLnet Labs组织的一款DNS服务器软件。 NLnet Labs NSD 4.3.7至4.15.1之前版本存在安全漏洞，该漏洞源于调试/非发布构建类型的NSD服务对特制的DNS Cookie选项消息处理不当，可能使远程客户端导致服务子进程崩溃，持续攻击可造成拒绝服务。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
NLnet Labs NSD 4.3.7 ~ 4.15.1 -

II. Public POCs for CVE-2026-19401

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III. Intelligence Information for CVE-2026-19401

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Other References for CVE-2026-19401 (1)

Same Patch Batch · NLnet Labs · 2026-08-26 · 4 CVEs total

CVE-2026-18664 8.2 HIGH Wrong interpretation of ACL ranges
CVE-2026-19538 8.2 HIGH Bypass of BLOCKED ACL items on proxy protocol port over TCP or TLS
CVE-2026-18916 6.9 MEDIUM Remote TCP DoS by throttling the TCP receive window

IV. Related Vulnerabilities

Same product: NSD
Same vendor: NLnet Labs
Same weakness: CWE-617

V. Comments for CVE-2026-19401

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