CVE-2026-33217 NATS allows MQTT clients to bypass ACL checks
Attackers can bypass Access Control Lists on MQTT subjects in NATS Server, allowing unauthorized access to restricted message streams.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-33217?
CVE-2026-33217 is a high-severity missing authorization vulnerability in nats-io nats-server, published on 25 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-33217?
9 open source packages ship an affected version, including github.com/nats-io/nats-server/v2, nats and github.com/nats-io/nats-server. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/nats-io/nats-server/v2 Go | All versions | 2.11.15, 2.12.6 |
github.com/nats-io/nats-server/v2 Go | All versions | 2.11.15 |
github.com/nats-io/nats-server/v2 Go | All versions | 2.11.15 |
github.com/nats-io/nats-server/v2 Go | From 2.12.0-RC.1 | 2.12.6 |
github.com/nats-io/nats-server/v2 Go | From 2.12.0-RC.1 | 2.12.6 |
nats Bitnami | All versions | 2.11.15, 2.12.6 |
3 more packages
github.com/nats-io/nats-server Go | All versions | None |
github.com/nats-io/nats-server Go | All versions | None |
github.com/nats-io/nats-server Go | All versions | None |
Products include Linuxfoundation Nats-Server.
How do I fix CVE-2026-33217?
Upgrade github.com/nats-io/nats-server/v2 to a fixed version for your release line: 2.11.15 or 2.12.6.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-33217 being exploited?
There is no known exploitation of CVE-2026-33217 in the wild and no public exploit code.
Other vulnerabilities in nats-io nats-server
- CVE-2022-28357 NATS nats-server allows directory traversal via unintended path to a management action
- CVE-2026-58253 NATS Server: Route API Auth Bypass
- CVE-2022-24450 Incorrect Authorization in NATS nats-server
- CVE-2026-33216 NATS has MQTT plaintext password disclosure
- CVE-2026-58207 NATS Server: Remote crash via integer overflow in Connz pagination
Sources
Also known as BIT-nats-2026-33217, CLEANSTART-2026-NP59628, DEBIAN-CVE-2026-33217, ECHO-1f93-d473-3105, GHSA-jxxm-27vp-c3m5, GO-2026-4834 and 10 more.