CVE-2026-58209: NATS Server: MQTT retained and QoS replay bypass subscribe deny filters
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.
Other sources
NATS Server: MQTT retained and QoS replay bypass subscribe deny filters
— Microsoft
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 1.31.0-24 - Upgrade
Upgrade
nats-serverto a version that resolves this vulnerability.Fixed in 2.14.3 - Upgrade
Upgrade
nats-serverto a version that resolves this vulnerability.Fixed in 2.12.12
Event History
Frequently Asked Questions
What is the severity of CVE-2026-58209?
The severity of CVE-2026-58209 is rated medium with a score of 4.3.
How do I fix CVE-2026-58209?
To fix CVE-2026-58209, upgrade to NATS Server version 2.14.3 or later or 2.12.12 or later.
What type of vulnerability is CVE-2026-58209?
CVE-2026-58209 is a vulnerability that involves an MQTT retained message delivery and QoS1+ durable replay bypass for subscribe deny filters.
What impact does CVE-2026-58209 have on NATS Server?
CVE-2026-58209 could allow messages to be delivered despite subscriber configured deny rules, potentially exposing sensitive information.
Which software versions are affected by CVE-2026-58209?
CVE-2026-58209 affects NATS Server versions prior to 2.14.3 and 2.12.12.