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Vulnerability · Published Mar 25, 2026 · Assigned by GitHub_M

CVE-2026-33248NATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching

Medium 4.2

In plain English

A medium-severity improper authentication in nats-server from nats-io. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 4% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)4.2Medium
Exploit odds (30 days)0.1%top 95.9% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Alpine:v3.23nats-server2.12.6-r0ALPINE-CVE-2026-33248
Alpine:v3.24nats-server2.12.6-r0ALPINE-CVE-2026-33248
Debian:12nats-serverno fix listedDEBIAN-CVE-2026-33248
Debian:13nats-serverno fix listedDEBIAN-CVE-2026-33248
Debian:14nats-server2.12.6-1DEBIAN-CVE-2026-33248
Gogithub.com/nats-io/nats-serverno fix listedGHSA-3f24-pcvm-5jqc
Gogithub.com/nats-io/nats-serverno fix listedGO-2026-4828
Gogithub.com/nats-io/nats-server/v22.12.6GHSA-3f24-pcvm-5jqc
Gogithub.com/nats-io/nats-server/v22.11.15GHSA-3f24-pcvm-5jqc
Gogithub.com/nats-io/nats-server/v22.11.15, 2.12.6GO-2026-4828
Ubuntu:24.04:LTSnats-serverno fix listedUBUNTU-CVE-2026-33248
Ubuntu:25.10nats-serverno fix listedUBUNTU-CVE-2026-33248
Ubuntu:26.10nats-serverno fix listedUBUNTU-CVE-2026-33248

Affected products (as reported)

VendorProductVersions
nats-io nats-server < 2.11.15>= 2.12.0-RC.1, < 2.12.6

Weakness: CWE-287, CWE-295 · Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N

References