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CVE-2026-33219
5.3 MEDIUM
- CVSS version: 3.1
- Attack vector (AV): NETWORK
- Attack complexity (AC): LOW
- Privileges required (PR): NONE
- User interaction (UI): NONE
- Scope (S): UNCHANGED
- Confidentiality impact (C): NONE
- Integrity impact (I): NONE
- Availability impact (A): LOW
NATS is vulnerable to pre-auth DoS through WebSockets client service
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, 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 CVE-2026-27571. That earlier issue was a compression bomb, this vulnerability is not. Attacks against this new issue thus require significant client bandwidth. Versions 2.11.15 and 2.12.6 contain a fix. As a workaround, disable websockets if not required for project deployment.
References
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https://github.com/nats-io/nats-server/security/advisories/GHSA-8r68-gvr4-jh7j x_refsource_CONFIRM
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https://advisories.nats.io/CVE/secnote-2026-02.txt x_refsource_MISC
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https://advisories.nats.io/CVE/secnote-2026-11.txt x_refsource_MISC
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https://github.com/advisories/GHSA-qrvq-68c2-7grw x_refsource_MISC
Affected products
nats-server
- ==< 2.11.15
- ==>= 2.12.0-RC.1, < 2.12.6
Package maintainers
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@derekcollison Derek Collison <derek@nats.io>
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@swdunlop Scott W. Dunlop <swdunlop@gmail.com>