NATS Server: MQTT subscribe ACL bypass via $MQTT.deliver.pubrel prefix (incomplete fix for CVE-2026-33217)
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, an authenticated MQTT client could subscribe to the internal $MQTT.deliver.pubrel subject family, bypassing configured subscribe permissions and exposing MQTT QoS2 protocol metadata for sessions in the account. This issue is fixed in versions 2.14.3 and 2.12.12.
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describes (1)
Related CVEs.
| ID | severity | exploitable | ||
|---|---|---|---|---|
| CVE-2026-58214US | —OT elevated | — | ||
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, an authenticated MQTT client could subscribe to the i… | ||||
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references
External citations — patches, advisories, analysis.
- https://github.com/nats-io/nats-server/commit/297b166be60fe13144084eed4b25201ead03204aFIX
- https://github.com/nats-io/nats-server/commit/34b09657bb596d5f850eaa5cfc97ea6b2f989a97FIX
- https://github.com/nats-io/nats-server/releases/tag/v2.12.12ARTICLE
- https://github.com/nats-io/nats-server/releases/tag/v2.14.3ARTICLE
- https://github.com/nats-io/nats-server/security/advisories/GHSA-4g68-3pwx-5vfjADVISORY
- https://nvd.nist.gov/vuln/detail/CVE-2026-58214WEB
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