| Package | Affected versions | Patched versions |
|---|---|---|
| github.com/nats-io/nats-server | all versions | |
| github.com/nats-io/nats-server/v2 | ≥ 2.12.0-RC.1, < 2.12.6< 2.11.15 | 2.12.62.11.15 |
| nats-server | ≥ 2.12.0, < 2.12.6< 2.11.15 | 2.12.62.11.15 |
NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing.
The nats-server offers a WebSockets client service, used in deployments where browsers are the NATS clients.
A malicious client which can connect to the WebSockets port can cause unbounded memory use in the nats-server before authentication; this requires sending a corresponding amount of data.
This is a milder variant of NATS-advisory-ID 2026-02 (aka CVE-2026-27571; GHSA-qrvq-68c2-7grw). That earlier issue was a compression bomb, this vulnerability is not. Attacks against this new issue thus require significant client bandwidth.
Any version before v2.12.6 or v2.11.15
Disable websockets if not required for project deployment.
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