CVE-2026-33216: NATS Server MQTT Plaintext Password Disclosure Vulnerability
Summary
CVE-2026-33216: NATS has MQTT plaintext password disclosure. Affects github.com/nats-io/nats-server/v2 across 2 version ranges.
< 2.11.15
>= 2.12.0-RC.1, < 2.12.6
Fixed in 2.11.15 or 2.12.6, depending on the release line you run. How to fix ↓
Also tracked for
- nats · Bitnami
- github.com/nats-io/nats-server · Go
The same CVE-2026-33216 is tracked separately for each ecosystem and vendor. Its fix information is the same; the package and affected versions differ.
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Background
NATS.io is a high-performance open-source pub-sub distributed communication technology designed for cloud, on-premise, IoT, and edge computing. The nats-server component provides an MQTT client interface, enabling efficient message communication. However, certain configurations expose sensitive information, leading to potential security risks.
Vulnerability Detail
The vulnerability arises from the incorrect classification of MQTT passwords as non-authenticating identity statements (JWT). This misclassification allows MQTT passwords to be exposed through monitoring endpoints, posing a significant risk of unauthorized access to sensitive data. Attackers could exploit this flaw to gain insights into user credentials, leading to further security breaches.
How To Fix
Latest published version: v2.15.1 as of 23 Oct 2026
go get github.com/nats-io/nats-server/v2@v2.15.1Upgrading to it may include breaking changes; the versions below are the minimum fixed release for this vulnerability.
If you can't move to the latest
The minimum fixed version depends on the release line you run.
-
< 2.11.152.11.15go get github.com/nats-io/nats-server/v2@v2.11.15 -
>= 2.12.0-RC.1, < 2.12.62.12.6go get github.com/nats-io/nats-server/v2@v2.12.6
Tip — Not sure which release line you're on? Vulert can find the fix for the version you are using. Scan free →
Workaround
Ensure that monitoring endpoints are adequately secured. It is recommended to restrict access to these endpoints and avoid exposing them to the Internet or untrusted networks.
Conclusion
The NATS Server vulnerability CVE-2026-33216 poses a significant risk by exposing MQTT plaintext passwords through monitoring endpoints. It is crucial to update to the latest patched versions and implement security measures to mitigate this risk.
See every vulnerability recorded for github.com/nats-io/nats-server/v2 →
FAQ
The vulnerability involves the exposure of MQTT plaintext passwords through monitoring endpoints due to incorrect classification.
Any version before v2.12.6 or v2.11.15 is affected by this vulnerability.
If exploited, attackers could gain access to sensitive MQTT passwords, leading to unauthorized access and potential data breaches.
You can use Vulert's playground at Vulert Scanner to check if your application is affected by this vulnerability without requiring any signup.
The CVSS score of this vulnerability is 8.6, indicating a high severity level.
Related vulnerabilities
Recent vulnerabilities recorded for github.com/nats-io/nats-server/v2.
