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CVE-2026-19538— Bypass of BLOCKED ACL items on proxy protocol port over TCP or TLS

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组织的一款权威域名解析服务器。 NLnet Labs NSD 4.8.0版本至4.15.1之前版本存在安全漏洞，该漏洞源于通过TCP或TLS连接时在保持连接的情况下发送两次查询，可完全绕过用于拒绝代理协议端口访问的BLOCKED访问控制列表项，导致认证绕过。

CVSS 8.2 · High EPSS 0.23% · P13

Affected Version Matrix 1

VendorProduct Version RangeStatus
NLnet Labs NSD 4.8.0< 4.15.1 affected
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I. Basic Information for CVE-2026-19538

Vulnerability Information
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Vulnerability Title
Bypass of BLOCKED ACL items on proxy protocol port over TCP or TLS
Source: CVE Program / CVE List V5
Vulnerability Description
The BLOCKED access control list items that are evaluated to deny access on the the proxy protocol port can be bypassed completely when connecting over TCP or TLS and sending the query twice on connection that is kept open.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
使用欺骗进行的认证绕过
Source: CVE Program / CVE List V5
Vulnerability Title
NLnet Labs NSD 授权问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
NLnet Labs NSD是荷兰NLnet Labs组织的一款权威域名解析服务器。 NLnet Labs NSD 4.8.0版本至4.15.1之前版本存在安全漏洞，该漏洞源于通过TCP或TLS连接时在保持连接的情况下发送两次查询，可完全绕过用于拒绝代理协议端口访问的BLOCKED访问控制列表项，导致认证绕过。
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 4.8.0 ~ 4.15.1 -

II. Public POCs for CVE-2026-19538

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III. Intelligence Information for CVE-2026-19538

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Other References for CVE-2026-19538 (1)

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

CVE-2026-18664 8.2 HIGH Wrong interpretation of ACL ranges
CVE-2026-19401 8.2 HIGH Remote UDP DoS by sending multiple DNS Cookie options
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-290

V. Comments for CVE-2026-19538

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