NATS Server: MQTT subscribe ACL bypass via $MQTT.deliver.pubrel prefix (incomplete fix for CVE-2026-33217)
13Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 4.3epss 0.3%
exploitation probability
0.3%top 83% of all CVEs
observed exploitation
nono source reports it
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.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Affected products
nats-io · nats-serverReferences
https://github.com/nats-io/nats-server/commit/297b166be60fe13144084eed4b25201ead03204ahttps://github.com/nats-io/nats-server/commit/34b09657bb596d5f850eaa5cfc97ea6b2f989a97https://github.com/nats-io/nats-server/releases/tag/v2.12.12https://github.com/nats-io/nats-server/releases/tag/v2.14.3https://github.com/nats-io/nats-server/security/advisories/GHSA-4g68-3pwx-5vfj