What is CVE-2026-33248?

CVE-2026-33248 is a medium-severity vulnerability in Nats-io Nats-server, classified under Improper Authentication. CVSS score: 4.2/10. Published 2026-03-25.

How severe is CVE-2026-33248?

Medium severity. CVSS v3 base score is 4.2 out of 10.

Auth bypass in Nats-io Nats-server

CVE-2026-33248

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, when using mTLS for client identity, with `verify_and_map` to derive a NATS identity from the client cert…

Vulnerability class: Broken Authentication

EPSS: 0.000 (0.9th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 4.2 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N.

Affected products

Nats-io Nats-server — versions < 2.11.15, >= 2.12.0-RC.1, < 2.12.6

Weakness classification (CWE)

References

https://github.com/nats-io/nats-server/security/advisories/GHSA-3f24-pcvm-5jqc (x_refsource_CONFIRM)
https://advisories.nats.io/CVE/secnote-2026-13.txt (x_refsource_MISC)

Frequently asked questions

What is CVE-2026-33248?: CVE-2026-33248 is a medium-severity vulnerability in Nats-io Nats-server, classified under Improper Authentication. CVSS score: 4.2/10. Published 2026-03-25.
How severe is CVE-2026-33248?: Medium severity. CVSS v3 base score is 4.2 out of 10.