CVE-2026-33248
MEDIUMCVSS Vector
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N
Lifecycle Timeline
3Description
### Background NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing. One authentication model supported is mTLS, deriving the NATS client identity from properties of the TLS Client Certificate. ### Problem Description 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. ### Affected Versions Fixed in nats-server 2.12.6 & 2.11.15 ### Workarounds Developers should review their CA issuing practices.
Analysis
NATS.io nats-server contains an authentication bypass vulnerability in its mTLS client identity verification when using the verify_and_map feature to derive NATS identities from TLS client certificate Subject DN patterns. An authenticated attacker with a valid certificate from a trusted CA can exploit certain RDN (Relative Distinguished Name) patterns to bypass intended identity mapping controls, potentially gaining unauthorized access to message queues. …
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Remediation
Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Audit authentication configurations.
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