CVE-2026-33248Medium· 4.2▾ SunlitNATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching
▾ Sunlit zone — Low / medium · no exploitation signal
impact 23.1 · likelihood 0 · exploitation 0
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Exploit-prediction probability, daily snapshots since Sep 12.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via OSV
Last analysed / modified upstream
0.1%
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.
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.
Fixed in nats-server 2.12.6 & 2.11.15
Developers should review their CA issuing practices.
github.com/nats-io/nats-server/v2 < 2.11.15github.com/nats-io/nats-server/v2 >= 2.12.0-RC.1, < 2.12.6github.com/nats-io/nats-serverUpgrade to a patched release:
github.com/nats-io/nats-server/v2 2.11.15github.com/nats-io/nats-server/v2 2.12.6Connected by shared product, vendor, weakness, or advisory.
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