CVE-2026-33248

NATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching

CVSS 3.1 4.2 MEDIUMEUVD CVSS 3.1 4.2 CVSS 3.1 · [email protected] · Secondary 4.2 MEDIUMCVSS_V3 Publisher rating MODERATEFixed by github.com/nats-io/nats-server/v2 2.11.15 Fixed by github.com/nats-io/nats-server/v2 2.12.6osv · severity unknownFixed by github.com/nats-io/nats-server/v2 2.11.15 Fixed by github.com/nats-io/nats-server/v2 2.12.6KEV status unknown

Original advisory

cve-program · CVE-2026-33248

Published

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.

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euvd · EUVD-2026-15999

Published

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nvd · CVE-2026-33248

Published

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osv · GHSA-3f24-pcvm-5jqc

Published

### 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.

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osv · GO-2026-4828

Published

NATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching in github.com/nats-io/nats-server

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Affected versions, risk and source history

Exploitation and risk

Source status

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Risk history

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Advisory history

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13 Nov 2026 20:09:47 UTC