CVE-2026-33248: medium-severity vulnerability in nats-io nats-server
NATS has mTLS verify_and_map authentication bypass via incorrect Subject DN matching
Published · Updated
E-mail alert when it lands in KEV, gets a public PoC or its score goes up.
13Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 4.2epss 0.1%
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.
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N
Affected products
nats-io · nats-serverRelated CVEs — nats-io nats-server
In the same product, most dangerous first.
CVE-2026-58210HIGHNATS Server: MQTT partial CONNECT packets can exhaust pre-auth memoryEPSS 0.7%CVE-2026-58250HIGHNATS Server: Pre-auth server crash via double INFO in leafnode handshakeEPSS 0.7%CVE-2026-29785HIGHNATS Server panic via malicious compression on leafnode portEPSS 0.7%CVE-2026-33218HIGHNATS has pre-auth server panic via leafnode handlingEPSS 0.6%CVE-2025-30215CRITICALNATS-Server Fails to Authorize Certain Jetstream Admin APIsEPSS 0.6%CVE-2026-58208MEDIUMNATS Server: MQTT-over-WebSocket Path Can Crash WebSocket-Only JetStream Servers Before MQTT Is EnabledEPSS 0.6%