Bug 2451450 (CVE-2026-33218)

Summary: CVE-2026-33218 nats-server: github.com/nats-io/nats-server: NATS-Server: Denial of Service via malformed message pre-authentication on leafnode port
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 high-performance messaging system. A remote attacker, by connecting to the leafnode port and sending a specially crafted malformed message before authentication, can cause the nats-server to crash. This vulnerability leads to a Denial of Service (DoS), making the server 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: 2451498    
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Description OSIDB Bzimport 2026-03-25 20:02:37 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 client which can connect to the leafnode port can crash the nats-server with a certain malformed message pre-authentication. Versions 2.11.15 and 2.12.6 contain a fix. As a workaround, disable leafnode support if not needed or restrict network connections to the leafnode port, if plausible without compromising the service offered.