4.2

CVE-2026-33248: linuxfoundation nats-server Improper Authentication

CVSS: 4.2v3.1MediumAnalyzed
AliasesUBUNTU-CVE-2026-33248DEBIAN-CVE-2026-33248CGA-2cv4-4rjc-g82j
Published 25-03-2026Last modified 26-03-2026
Open JSON

Vulnerability summary

CVE-2026-33248 is a medium (CVSS 4.2) Improper Authentication vulnerability in linuxfoundation nats-server. EPSS estimates a 0.17% chance of exploitation in the next 30 days, higher than 5.9% of scored vulnerabilities.

Overall risk
17/100
0100
Low · default modelHow is this calculated?
CVSS score
4.2/10
010
Medium · v3.1 (CVE.org)
EPSS score
0.17%
0%100%
Low · +0.03 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 2 · Related 3
OPENSUSE-SU-2026:21483-1SUSE-SU-2026:1135-1CGA-MVV8-7788-XF2R

Timeline

  1. 25-03-2026
    PublishedVulnerability first disclosed.
  2. 26-03-2026
    Last modifiedVulnerability information updated.

Description

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 certificate's Subject DN, certain patterns of RDN would not be correctly enforced, allowing for authentication bypass. This does require a valid certificate from a CA already trusted for client certificates, and `DN` naming patterns which the NATS maintainers consider highly unlikely. So this is an unlikely attack. Nonetheless, administrators who have been very sophisticated in their `DN` construction patterns might conceivably be impacted. Versions 2.11.15 and 2.12.6 contain a fix. As a workaround, developers should review their CA issuing practices.

CVSS metrics

7 scores · 7 sources · 1 version

EPSS trend

Probability

0.17%

Chance of exploitation in the next 30 days

Percentile

6%

Versus all other CVEs

30-day change

+0.03 pp

From 0.14% on 20-09-2026

20-09-202620-10-2026
EPSS score
0.17%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Chainguard28 products
  • k3s< 1.35.2.1-r4
  • k3s-1.32< 1.32.13.1-r7
  • k3s-1.33< 1.33.9.1-r6
  • k3s-static< 1.35.2.1-r4
  • k3s-static-1.32< 1.32.13.1-r7
Wolfi12 products
  • k3s< 1.35.2.1-r4
  • k3s-1.32< 1.32.13.1-r7
  • k3s-1.33< 1.33.9.1-r6
  • k3s-static< 1.35.2.1-r4
  • k3s-static-1.32< 1.32.13.1-r7
Debian1 product
  • nats-serverAll versions (No fix recorded) | < 2.12.6-1
Github.com/nats-io1 product
  • nats-serverAll versions (No fix recorded)
Github.com/nats-io/nats-server1 product
  • v2< 2.11.15 | ≥ 2.12.0-RC.1, < 2.12.6
Linuxfoundation1 product
Nats-io1 product
Ubuntu1 product
  • nats-serverAll versions (No fix recorded)

8 vendors · 46 products

References

8 links