Bug 2451445 (CVE-2026-33219)

Summary: CVE-2026-33219 github.com/nats-io/nats-server: NATS-Server: Denial of Service via unbounded memory use in WebSockets
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: alcohan, gparvin, jbalunas, pahickey, rhaigner
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in NATS-Server. A malicious client connecting to the WebSockets port can cause unbounded memory use before authentication by sending a large amount of data. This resource exhaustion vulnerability can lead to a Denial of Service (DoS) for the server, making it unavailable to legitimate users.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Bug Depends On: 2451494    
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Description OSIDB Bzimport 2026-03-25 20:02:06 UTC
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.