CVE-2026-33219
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.
Does this matter?
Lower severity and a low EPSS score (0.53%). Track it; it rarely justifies an emergency change on its own.
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 3.1
- 5.3 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- EPSS
- 0.53% probability · 43th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-770
- Affected
- linuxfoundation/nats-server
- Source
- security-advisories@github.com
References
- https://advisories.nats.io/CVE/secnote-2026-02.txtMitigation, Vendor Advisory
- https://advisories.nats.io/CVE/secnote-2026-11.txtMitigation, Vendor Advisory
- https://github.com/advisories/GHSA-qrvq-68c2-7grwMitigation, Vendor Advisory
- https://github.com/nats-io/nats-server/security/advisories/GHSA-8r68-gvr4-jh7jMitigation, Vendor Advisory
- https://access.redhat.com/errata/RHSA-2026:21769
- https://access.redhat.com/errata/RHSA-2026:22347
- https://access.redhat.com/errata/RHSA-2026:23345
- https://access.redhat.com/security/cve/CVE-2026-33219
- https://bugzilla.redhat.com/show_bug.cgi?id=2451445
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33219.json
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.