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CVE-2026-58211

NATS Server: `no_auth_user` pre-CONNECT fast path bypasses user connection restrictions

5.4 MediumFix available

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, a client could be registered as the configured no_auth_user through a parser path used when the first client operation was not CONNECT, bypassing user-level connection restrictions such as allowed_connection_types or proxy_required that normal authentication would apply. This issue is fixed in versions 2.14.3 and 2.12.12.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
Low
User interaction
None

What an attacker can affect

Confidentiality
Low
Integrity
Low
Availability
None

Exploit likelihood

0.29%Unchanged since Jul 9, 2026
90%50%10%1%

What each source reports

CVE List Score used 5.4

NATS Server: `no_auth_user` pre-CONNECT fast path bypasses user connection restrictions

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, a client could be registered as the configured no_auth_user through a parser path used when the first client operation was not CONNECT, bypassing user-level connection restrictions such as allowed_connection_types or proxy_required that normal authentication would apply. This issue is fixed in versions 2.14.3 and 2.12.12.

Record
CVE-2026-58211
CVSS 3.1
5.4 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Weakness
CWE-863
Updated
2026-11-02
EUVDEUVD-2026-42390 5.4

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, a client could be registered as the configured no_auth_user through a parser path used when the first client operation was not CONNECT, bypassing user-level connection restrictions such as allowed_connection_types or proxy_required that normal authentication would apply. This issue is fixed in versions 2.14.3 and 2.12.12.

Record
EUVD-2026-42390
CVSS 3.1
5.4 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Updated
2026-11-02
NVD 5.4

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, a client could be registered as the configured no_auth_user through a parser path used when the first client operation was not CONNECT, bypassing user-level connection restrictions such as allowed_connection_types or proxy_required that normal authentication would apply. This issue is fixed in versions 2.14.3 and 2.12.12.

Record
CVE-2026-58211
CVSS 3.1
5.4 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Weakness
CWE-863
Updated
2026-11-02
OSV 5.4

NATS Server: `no_auth_user` pre-CONNECT fast path bypasses user connection restrictions

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, a client could be registered as the configured no_auth_user through a parser path used when the first client operation was not CONNECT, bypassing user-level connection restrictions such as allowed_connection_types or proxy_required that normal authentication would apply. This issue is fixed in versions 2.14.3 and 2.12.12.

Record
CVE-2026-58211
CVSS 3.1
5.4 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Weakness
CWE-863
Updated
2026-11-02
OSVDEBIAN-CVE-2026-58211 5.4

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, a client could be registered as the configured no_auth_user through a parser path used when the first client operation was not CONNECT, bypassing user-level connection restrictions such as allowed_connection_types or proxy_required that normal authentication would apply. This issue is fixed in versions 2.14.3 and 2.12.12.

Record
DEBIAN-CVE-2026-58211
CVSS 3.1
5.4 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Updated
2026-11-02
OSVRHSA-2026:36016 7.5

Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update

Record
RHSA-2026:36016
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVRHSA-2026:36017 7.5

Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update

Record
RHSA-2026:36017
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVUBUNTU-CVE-2026-58211 5.4

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, a client could be registered as the configured no_auth_user through a parser path used when the first client operation was not CONNECT, bypassing user-level connection restrictions such as allowed_connection_types or proxy_required that normal authentication would apply. This issue is fixed in versions 2.14.3 and 2.12.12.

Record
UBUNTU-CVE-2026-58211
CVSS 3.1
5.4 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
nats-server
Debian:12
 All versions, plus listed versions
2.10.1-12.10.16-12.10.18-12.10.24-12.10.27-1
Show 11 moreShow less
2.10.3-12.10.4-12.10.7-12.12.4-12.12.6-12.14.1-12.14.3-12.14.6-12.15.1-12.9.10-12.9.19-1
 None known
nats-server
Debian:13
 All versions, plus listed versions
2.10.27-12.12.4-12.12.6-12.14.1-12.14.3-12.14.6-12.15.1-1
 None known
nats-server
Debian:14
 before 2.14.3-1, plus listed versions
2.10.27-12.12.4-12.12.6-12.14.1-1
2.14.3-1
nats-server2.14
Red Hat:hummingbird:1
From an advisory covering 6 CVEs
 before 0:2.14.3-1.hum1
0:2.14.3-1.hum1
nats-server2.12
Red Hat:hummingbird:1
From an advisory covering 6 CVEs
 before 0:2.12.12-1.hum1
0:2.12.12-1.hum1
nats-server
Ubuntu:24.04:LTS
 All versions, plus listed versions
2.9.19-1build12.10.3-12.10.4-12.10.7-12.10.7-1ubuntu0.12.10.7-1ubuntu0.22.10.7-1ubuntu0.3
 None known
nats-server
Ubuntu:25.10
 All versions, plus listed versions
2.10.24-12.10.27-1
 None known
nats-server
Ubuntu:26.10
 All versions, plus listed versions
2.10.27-1build12.14.1-12.14.3-1
 None known
nats-server
Ubuntu:Pro:26.04:LTS
 All versions, plus listed versions
2.10.27-12.10.27-1build12.10.27-1ubuntu0.26.04.1~esm1
 None known

History

History
RecordedChangedSources
affected, facts
first indexedCVE List, EUVD, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-58211 is a medium vulnerability (CVSS 5.4) in Linuxfoundation Nats-server, published July 8, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.29%, the 21st percentile. Fixed in nats-server 2.14.3-1.

References

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