CVE-2026-58211: medium-severity vulnerability in nats-io nats-server
NATS Server: `no_auth_user` pre-CONNECT fast path bypasses user connection restrictions
Published · Updated
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13Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 5.4epss 0.3%
NATS Server is a high-performance server for NATS.io, the cloud and edge native messaging system. Prior to 2.14.3 and 2.12.12, a client could be registered as the configured no_auth_user through a parser path used when the first client operation was not CONNECT, bypassing user-level connection restrictions such as allowed_connection_types or proxy_required that normal authentication would apply. This issue is fixed in versions 2.14.3 and 2.12.12.
CVSS:3.1/AV:N/AC:L/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%