CVE-2026-33217highCWE-425CWE-863

CVE-2026-33217: high-severity vulnerability in nats-io nats-server

NATS allows MQTT clients to bypass ACL checks

Published · Updated

Follow this CVE+ Monitor nats-server+ Monitor nats-server

E-mail alert when it lands in KEV, gets a public PoC or its score goes up.

21Vexday Risk Score

No sign of exploitation. No public exploitation artifact known so far.

ssvc Trackcvss 7.1epss 0.3%
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 ACLs on message subjects, these ACLs were not applied in the `$MQTT.>` namespace, allowing MQTT clients to bypass ACL checks for MQTT subjects. Versions 2.11.15 and 2.12.6 contain a fix. No known workarounds are available.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N
Affected products
nats-io · nats-server
Related 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%