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Vulnerability record · CVE-2026-19538 · published 26 August 2026

CVE-2026-19538: Nlnetlabs nsd authentication bypass by spoofing vulnerability

Nlnetlabs · Nsd

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.

8.2 CVSS 4.0 High EPSS 0.23% · top 87.3% CWE-290 · Authentication bypass by spoofingCWE-672 · CWE-672
8.2CVSS 4.0 base score
0.23%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
1References
8 Sep 2026Last modified by NVD

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.

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/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:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-19538.txt Vendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

8.7CVE-2026-12245Nlnetlabs nsd use after free vulnerabilityNSD from version 4.13.0 has a heap use-after-free bug in logging errors on TLS connections, causing a crash of the server process, which can be trigg…EPSS 0.46%8.7CVE-2026-12244Nlnetlabs nsd heap-based buffer overflow vulnerabilityIf NSD is configured as secondary for a zone, the primary of that zone can crash NSD with an AXFR containing a DNS message with a special crafted SVC…EPSS 0.49%8.2CVE-2026-18664Nlnetlabs nsd improper access control vulnerabilityWhen ranges are used for access control (i.e. of the form 1.2.3.4-1.2.3.25), because NSD wrongly compares the IP address with the range on little end…EPSS 0.26%8.2CVE-2026-19401Nlnetlabs nsd uncontrolled resource consumption vulnerabilityAny remote client can crash a (debugging/non-release build type) NSD serve child by sending it a special crafted message with a specially tuned numbe…EPSS 0.28%8.2CVE-2026-12490Nlnetlabs nsd improper access control vulnerabilityWhen a provide-xfr is given with a tls-auth-name, a secondary requesting a transfer should provide a client certificate with that name. However, no c…EPSS 0.22%7.5CVE-2016-6173Nlnetlabs nsd vulnerabilityNSD before 4.1.11 allows remote DNS master servers to cause a denial of service (/tmp disk consumption and slave server crash) via a zone transfer wi…EPSS 2.9%7.2CVE-2026-12246Nlnetlabs nsd improper input validation vulnerabilityNSD version 4.14.0 introduced a bug where a specially crafted APL RR, with an adflength larger than permitted for the address family will overwrite t…EPSS 0.44%6.9CVE-2026-18916Nlnetlabs nsd vulnerabilityAny remote client can crash a NSD serve child, by throttling the TCP receive window after a TCP query. By continuously crashing the serve childs, the…EPSS 0.28%

Source: NIST National Vulnerability Database (record CVE-2026-19538), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.