BlackTreeIndependent security intelligence

Full vulnerability report · 2026

CVE-2026-58211High confidence

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

nats-io · nats-server

5.4MediumCVSS 3.1

Recommended action

Scheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available

Distribution package intelligence

Ubuntu vendor package status

Canonical’s release and source-package findings are shown separately from local repository availability.

1 package state

Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Ubuntu release	Source package	Vendor state	Fixed version	Evidence
Ubuntu 24.04 LTSnoble · standard archive	`nats-server`	Under evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.	`Not published in this feed`	Canonical record ↗Source updated 9 Sept 2026

Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current

CVE-2026-58211 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitynats-server: NATS Server: Authentication bypass allows unauthorized access and information disclosure

6 fixed

The vendor explicitly identifies these products or versions as containing the fix.

nats-server2-12-main@aarch64 as a component of Red Hat Hardened Images
nats-server2-12-main@src as a component of Red Hat Hardened Images
nats-server2-12-main@x86_64 as a component of Red Hat Hardened Images
nats-server2-14-main@aarch64 as a component of Red Hat Hardened Images
nats-server2-14-main@src as a component of Red Hat Hardened Images
nats-server2-14-main@x86_64 as a component of Red Hat Hardened Images

Summary: A flaw was found in NATS Server, a high-performance messaging system. This vulnerability allows a client to bypass normal authentication and connection restrictions by registering as a "no_auth_user" through a specific parser path. This occurs when the client's initial operation is not a standard connection request. The consequence is unauthorized access, potentially leading to information disclosure or other unauthorized actions within the messaging system.
Remediation: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current

ENISA EUVD identifier

EUVD-2026-42390

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state: Present in the current official mapping
Known exploitation: Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score: Not supplied in the stored EUVD record
Advisory evidence: No linked advisory details stored yet

Recommended actionScheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available

What, why and how

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.

What

Why

The application performs an authorisation check, but it does not correctly enforce the required permission boundary.

How

An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

Why

The application performs an authorisation check, but it does not correctly enforce the required permission boundary.

How

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation

Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.

No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material

Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.

None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path: a network path → Incorrect Authorization → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface: Network
Privileges required: Low: a basic authenticated account is required
User interaction: None
Attack complexity: Low: no specialised conditions are recorded
Security boundary: Unchanged: impact remains within the vulnerable component's security authority
Weakness ? CWE means Common Weakness Enumeration: a standard category for the underlying weakness.: CWE-863 ↗
CWE-863: Incorrect Authorization. The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
CVSS vector ? CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRLowPrivileges required: The attacker needs basic user-level privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CLowConfidentiality impact: A successful attack can cause a limited loss.ILowIntegrity impact: A successful attack can cause a limited loss.ANoneAvailability impact: No direct loss is represented by this metric.
Post-exploitation / living off the land: No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.

NetworkCWE-863

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-42390Official EUVD mapping

0 linked advisory records.

Official EUVD record

BSI · German · WID-SEC-W-2026-2132NATS Server: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in NATS Server ausnutzen, um beliebigen Programmcode auszuführen, erweiterte Berechtigungen zu erlangen, Sicherheitsmaßnahmen zu umgehen, Daten zu manipulieren oder offenzulegen oder einen Denial-of-Service-Zustand zu verursachen.

Official advisory

Patch and workaround

Operational remediation based on structured source evidence.

Status ? Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.: Patch available
Affected: < 2.12.12; >= 2.14.0-RC.1, < 2.14.3
Fixed: nats-server2-12-main@aarch64 as a component of Red Hat Hardened Images; nats-server2-12-main@src as a component of Red Hat Hardened Images; nats-server2-12-main@x86_64 as a component of Red Hat Hardened Images; nats-server2-14-main@aarch64 as a component of Red Hat Hardened Images; nats-server2-14-main@src as a component of Red Hat Hardened Images; nats-server2-14-main@x86_64 as a component of Red Hat Hardened Images
Action: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/
Workaround: A mitigation or workaround reference is available from the source linked below; validate it against the affected product and version.

Evidence and provenance

Published 8 Jul 2026 · Last source change 9 Jul 2026, 14:27 UTC · CWE-863 · Incorrect Authorization

CVE recordCVE.org · 5.2

CVSS sourceCNA

EPSS source

The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.

FIRST · tracked since 2026-08-14

European sourceENISA EUVD · EUVD-2026-42390

Product sourceCNA

Remediation sourceVendor CSAF · Red Hat Product Security

CWE sourceCNA

NVD statusNVD enriched

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates →

No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.

2026-07-08CVE published

2026-07-09Mitigation reference recorded

ENISA EUVD · EUVD-2026-42390↗Vendor CSAF · Red Hat Product Security↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗

Technical terms and abbreviations used in this report

CVE: Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS: Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS: Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE: Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA: CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP: Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD: National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT: A computer security incident response team that publishes warnings or coordinates incident response.
PoC: Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF: Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL: Living off the land: abuse of legitimate tools or system functions during an attack.