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.
Affected products
linuxfoundation: nats-server
References10
- advisories.nats.io/CVE/secnote-2026-02.txt MitigationVendor Advisory
- advisories.nats.io/CVE/secnote-2026-11.txt MitigationVendor Advisory
- github.com/advisories/GHSA-qrvq-68c2-7grw MitigationVendor Advisory
- github.com/nats-io/nats-server/security/advisories/GHSA-8r68-gv… MitigationVendor Advisory
- access.redhat.com/errata/RHSA-2026:21769
- access.redhat.com/errata/RHSA-2026:22347
- access.redhat.com/errata/RHSA-2026:23345
- access.redhat.com/security/cve/CVE-2026-33219
- bugzilla.redhat.com/show_bug.cgi?id=2451445
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33219…
Metrics
- CVSS 3.1
-
5.3
MEDIUM
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - EPSS — exploit probability
- 1% percentile: 47 · as of 12 November 2026
- CWE
- CWE-770
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