CVE-2026-33248: Linuxfoundation Nats-Server

Medium severity, CVSS 4.2. EPSS: 0.2% chance of exploitation in the next 30 days.

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 products

• Linuxfoundation Nats-Server: before 2.11.15 (fixed in 2.11.15); from 2.12.0, before 2.12.6 (fixed in 2.12.6)

Published 2026-03-25. Last modified 2026-06-17.