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Fencer Vulns
medium 4.2

CVE-2026-33248 json

NATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching

published 2026-03-24 7 mo ago modified 2026-09-10 1 mo ago also BIT-nats-2026-33248 , EUVD-2026-15999 , GHSA-3f24-pcvm-5jqc , GO-2026-4828 , JLSEC-2026-1132

cvss
4.2
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.1%
EPSS 0.1% chance of exploitation in 30 days, percentile 4%
public exploits
0
none known

Summary

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.

Patch / fix

  • go github.com/nats-io/nats-server/v2 2.11.15, 2.12.6
  • bitnami nats 2.11.15, 2.12.6
  • julia nats_server_jll 2.14.3+0
  • linuxfoundation nats-server 2.11.15, 2.12.6
  • nats nats_server 2.11.15, 2.12.6
  • nats nats_streaming_server 2.11.15, 2.12.6
  • nats-server Debian 14 2.12.6-1

debian advisories DEBIAN-CVE-2026-33248

  • govulncheck-vulndb openSUSE Leap 15.6 0.0.20260326T203309-150000.1.155.2

suse advisories SUSE-SU-2026:1135-1

  • govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1

opensuse advisories openSUSE-SU-2026:21483-1

  • nats-server Alpine 3.24, Alpine 3.23 2.12.6-r0

alpine advisories ALPINE-CVE-2026-33248

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-33248 updated cvss 4.8

github.com/nats-io/nats-server: nats: NATS-Server: Authentication bypass due to incorrect Subject DN matching during mTLS client identity verification

  • Red Hat Multicluster Global Hub multicluster-globalhub/multicluster-globalhub-grafana-rhel9 Red Hat OpenShift Container Platform 4 openshift4/oc-mirror-plugin-rhel9
    affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
7 mo ago

Exploit prediction

0.15% chance of exploitation in the next 30 days, higher than 4% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 4.2 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N
GitHub 3.1 4.2 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N
OSV 3.1 4.2 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
go github.com/nats-io/nats-server/v2
<2.11.15
>=2.12.0-RC.1, <2.12.6
2.11.15
2.12.6
go github.com/nats-io/nats-server
all versions
 no fix listed
bitnami nats
<2.11.15
>=2.12.0, <2.12.6
2.11.15
2.12.6
julia nats_server_jll
<2.14.3+0
2.14.3+0

Affected products

  • nats-io nats-server

Classification

Weakness
  • CWE-287 Improper Authentication
  • CWE-295 Improper Certificate Validation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.