CVE-2026-33248

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.

How to fix CVE-2026-33248

To remediate CVE-2026-33248, upgrade the affected package to a fixed version below.

• —upgrade to 2.11.15 or later
• —no fix listed
• —no fix listed
• —no fix listed
• —upgrade to 2.11.15 or later
• —upgrade to 2.11.15 or later

Is CVE-2026-33248 being exploited?

Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.

Affected packages (6)

• from 0, < 2.11.15, >= 2.12.0, < 2.12.6
• from 0
• from 0
• from 0
• from 0, < 2.11.15
• from 0, < 2.11.15, >= 2.12.0-RC.1, < 2.12.6

CVSS scores

References (5)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2026-33248
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2026-33248
• PATCHgithub.com/nats-io/nats-server
• WEBadvisories.nats.io/CVE/secnote-2026-13.txt
• WEB