CVE-2026-58209
NATS Server: MQTT retained and QoS replay bypass subscribe deny filters
4.3
MEDIUM
CVSS 3.1
EPSS 0.34%
Description
NATS Server is a high-performance server for NATS.io, the cloud and edge native messaging system. Prior to 2.14.3 and 2.12.12, MQTT retained message delivery and QoS1+ durable replay could deliver messages whose original topics matched a subscriber configured subscribe deny rule because these delivery paths did not consistently recheck the concrete original topic before sending the MQTT PUBLISH to the subscriber. This issue is fixed in versions 2.14.3 and 2.12.12.
How to fix CVE-2026-58209
To remediate CVE-2026-58209, upgrade the affected package to a fixed version below.
- —upgrade to 2.12.12 or later
Is CVE-2026-58209 being exploited?
Low — EPSS is 0.3%, meaning exploitation activity has not been observed at scale.
Affected packages (1)
- from 0, < 2.12.12, >= 2.14.0, < 2.14.3
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | MEDIUM4.3 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N |