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NVD / CVE Program· CNA GitHub_M

CVE-2026-58211: NATS Server: `no_auth_user` pre-CONNECT fast path bypasses user connection restrictions

Noroxi assessment

Priority: Monitor (action score 21/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.29% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: nats-server (Debian:14) 2.14.3-1; nats-server2.12 (Red Hat:hummingbird:1) 0:2.12.12-1.hum1; nats-server2.14 (Red Hat:hummingbird:1) 0:2.14.3-1.hum1.

Low priority for now. Upgrade to nats-server (Debian:14) 2.14.3-1; nats-server2.12 (Red Hat:hummingbird:1) 0:2.12.12-1.hum1; nats-server2.14 (Red Hat:hummingbird:1) 0:2.14.3-1.hum1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

MediumCVSS 5.4 · v3.1—No exploit Fix available
Published
Jul 8, 2026
Updated
Oct 25, 2026
EPSS
0.2% · 21th percentile

Report tools

JSON

Action score

21

Monitor

Low priority for now.

CVSS
21 / 40 · 5.4 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · GitHub_M
5.4
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

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When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
linuxfoundationnats-server

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linuxfoundation nats-server2.12.0 and later · before 2.12.12
  • linuxfoundation nats-server2.14.0 and later · before 2.14.3

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

  • nats-io nats-server

    • < 2.12.12, >= 2.14.0-RC.1, < 2.14.3affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12nats-serverfrom 0—
Debian:14nats-serverbefore 2.14.3-12.14.3-1
Red Hat:hummingbird:1nats-server2.12before 0:2.12.12-1.hum10:2.12.12-1.hum1
Red Hat:hummingbird:1nats-server2.14before 0:2.14.3-1.hum10:2.14.3-1.hum1

Same product

linuxfoundation: all records

Other highest-scoring records for the same primary product.

  • CVE-2020-26892The JWT library in NATS nats-server before 2.1.9 has Incorrect Access Control because of how expired credentials are handled.
    40Plan
  • CVE-2022-28357NATS nats-server 2.2.0 through 2.7.4 allows directory traversal because of an unintended path to a management action from a management accou
    39Monitor
  • CVE-2026-58253NATS Server: Route API Auth Bypass
    35Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2026-58254Jul 8, 2026 · NATS Server: Incomplete fix for CVE-2026-33249: Leaf node connections bypass Nats-Trace-Dest permission check
    21Monitor
  • ← EarlierCVE-2026-58207Jul 8, 2026 · NATS Server: Remote crash via integer overflow in Connz pagination
    26Monitor
  • ← EarlierCVE-2026-58208Jul 8, 2026 · NATS Server: MQTT-over-WebSocket Path Can Crash WebSocket-Only JetStream Servers Before MQTT Is Enabled
    30Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
debian:nats-server2.14.3-1 · Debian:14Package registry (OSV)
red hat:nats-server2.120:2.12.12-1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:nats-server2.140:2.14.3-1.hum1 · Red Hat:hummingbird:1Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-33217105 days apartNATS allows MQTT clients to bypass ACL checks
    26Monitor
  • CVE-2026-582540 days apartNATS Server: Incomplete fix for CVE-2026-33249: Leaf node connections bypass Nats-Trace-Dest permission check
    21Monitor
  • CVE-2026-582090 days apartNATS Server: MQTT retained and QoS replay bypass subscribe deny filters
    17Monitor
  • CVE-2026-582140 days apartNATS Server: MQTT subscribe ACL bypass via $MQTT.deliver.pubrel prefix (incomplete fix for CVE-2026-33217)
    17Monitor
  • CVE-2026-33249105 days apartNATS: Message tracing can be redirected to arbitrary subject
    17Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
low · data can be read
Integrity
low · data or configuration can be modified
Availability
none
Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
Low
Integrity impact
Low
Availability impact
None

Weakness class (CWE)

CWE-863 · Incorrect Authorization

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records