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Medium severity · published Jul 8, 2026
CVE-2026-58214
NATS Server: MQTT subscribe ACL bypass via $MQTT.deliver.pubrel prefix (incomplete fix for CVE-2026-33217)
4.3
CVSS
0.3%
EPSS
No
On KEV
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, 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 vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
Low
Integrity
None
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 28% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
NA
nats-server · nats-io
< 2.12.12; >= 2.14.0-RC.1, < 2.14.3 · source: vendor, NVD
Affected product
NA
nats-server
nats-io
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-58214
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-58214
Patch
https://github.com/nats-io/nats-server/commit/297b166be60fe13144084eed4b25201ead03204a
Patch
https://github.com/nats-io/nats-server/commit/34b09657bb596d5f850eaa5cfc97ea6b2f989a97
Release Notes
https://github.com/nats-io/nats-server/releases/tag/v2.12.12
Release Notes
https://github.com/nats-io/nats-server/releases/tag/v2.14.3
Vendor Advisory
https://github.com/nats-io/nats-server/security/advisories/GHSA-4g68-3pwx-5vfj
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