What is CVE-2026-19538?

CVE-2026-19538 is a high-severity vulnerability in Nlnet Labs Nsd, classified under Authentication Bypass by Spoofing. CVSS score: 7.5/10. Published 2026-08-26.

How severe is CVE-2026-19538?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Nlnet Labs Nsd

CVE-2026-19538

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.

Published 2026-08-26 · last modified 2026-09-08.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.

EPSS exploit prediction

EPSS: 0.002 (13.0th percentile), scored 2026-10-11.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 13th percentile — 13.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.002 · change: -0.001

Affected products

Weakness classification (CWE)

References

www.nlnetlabs.nl/downloads/nsd/CVE-2026-19538.txt (vendor-advisory, Vendor Advisory)

Frequently asked questions

What is CVE-2026-19538?: CVE-2026-19538 is a high-severity vulnerability in Nlnet Labs Nsd, classified under Authentication Bypass by Spoofing. CVSS score: 7.5/10. Published 2026-08-26.
How severe is CVE-2026-19538?: High severity. CVSS v3 base score is 7.5 out of 10.