Medium severity · published Mar 25, 2026
CVE-2026-33219
NATS is vulnerable to pre-auth DoS through WebSockets client service
5.3
CVSS
0.5%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
Low
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.5% · higher than 46% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
NA
nats-server · nats-io
< 2.11.15; >= 2.12.0-RC.1, < 2.12.6 · source: vendor, NVD
MG
Multicluster Global Hub 1.4.5 · Red Hat
All versions, or not specified · source: CISA
MG
Multicluster Global Hub 1.6.5 · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat multicluster global hub 1.5.3 · Red Hat
All versions, or not specified · source: CISA
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-33219
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-33219
Mitigation
https://advisories.nats.io/CVE/secnote-2026-02.txt
Mitigation
https://advisories.nats.io/CVE/secnote-2026-11.txt
Mitigation
https://github.com/advisories/GHSA-qrvq-68c2-7grw
Mitigation
https://github.com/nats-io/nats-server/security/advisories/GHSA-8r68-gvr4-jh7j
access.redhat.com
https://access.redhat.com/errata/RHSA-2026:21769
access.redhat.com
https://access.redhat.com/errata/RHSA-2026:22347
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