Bug 2451447 (CVE-2026-27889)

Summary:	CVE-2026-27889 github.com/nats-io/nats-server: NATS-Server: Denial of Service via malformed WebSockets frame
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	alcohan, gparvin, jbalunas, pahickey, rhaigner
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
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Doc Text:	A flaw was found in NATS-Server, a high-performance messaging system. A remote attacker can exploit this vulnerability before authentication by sending a specially crafted WebSockets frame. This missing sanity check can trigger a server panic, leading to a Denial of Service (DoS) for affected deployments that use WebSockets and expose the network port to untrusted endpoints.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	2451496
Bug Blocks:

Description OSIDB Bzimport 2026-03-25 20:02:21 UTC

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Starting in version 2.2.0 and prior to versions 2.11.14 and 2.12.5, a missing sanity check on a WebSockets frame could trigger a server panic in the nats-server.  This happens before authentication, and so is exposed to anyone who can connect to the websockets port. Versions 2.11.14 and 2.12.5 contains a fix. A workaround is available. The vulnerability only affects deployments which use WebSockets and which expose the network port to untrusted end-points. If one is able to do so, a defense in depth of restricting either of these will mitigate the attack.