CVSS 3.1
5.3 mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:LCVE-2026-33219
Medium (5.3) in linuxfoundation nats-server. EPSS 0.5% chance of exploitation in the next 30 days. Fixed in github.com/nats-io/nats-server/v2 2.11.15, 2.12.6.
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.
Severity
- EPSS
- 0.5% chance of exploitation in the next 30 days; higher than 45% of CVEs (scores of 2026-10-31)
- CWE
- CWE-770
- Published
- Modified
- Record from
- the NVD, synced
Affected
- linuxfoundation:nats-server
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-8r68-gvr4-jh7j | Go | github.com/nats-io/nats-server/v2 | <2.11.15 | 2.11.15 |
| GHSA-8r68-gvr4-jh7j | Go | github.com/nats-io/nats-server/v2 | >=2.12.0-RC.1 <2.12.6 | 2.12.6 |
| GHSA-8r68-gvr4-jh7j | Go | github.com/nats-io/nats-server | all versions | no fix published |
| GO-2026-4831 | Go | github.com/nats-io/nats-server | all versions | no fix published |
| GO-2026-4831 | Go | github.com/nats-io/nats-server/v2 | <2.11.15 >=2.12.0-RC.1 <2.12.6 | 2.11.15, 2.12.6 |