Medium Authentication

CVE-2026-33246 — NATS: Leafnode connections allow spoofing of Nats-Request-Info identity headers

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. The nats-server offers a `Nats-Request-Info:` message header, providing information about a request. This is supposed to provide enough information to allow for account/user identification, such that NATS clients could make their own decisions on how to trust a message, provided that they trust the nats-server as a broker. A leafnode connecting to a nats-server is not fully trusted unless the system account is bridged too. Thus identity claims should not have propagated unchecked. Prior to versions 2.11.15 and 2.12.6, NATS clients relying upon the Nats-Request-Info: header could be spoofed. This does not directly affect the nats-server itself, but the CVSS Confidentiality and Integrity scores are based upon what a hypothetical client might choose to do with this NATS header. Versions 2.11.15 and 2.12.6 contain a fix. No known workarounds are available.

Published Mar 25, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: GitHub_M

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.2% (30-day exploitation probability)+2
Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.24%

ahead of 14% of scored CVEs · Oct 14, 2026

Affects

Linuxfoundation

Nats-server

CVSS base

5.4

Medium · 3 source(s)

Prioritization reference: 6.4 provisional

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

None

none · proof-of-concept · active

Automatable

can an attacker script the kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Linuxfoundation Nats-server, Nats-io Nats-server).
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes matching the vulnerability class (authentication), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Linuxfoundation	Nats-server	< 2.11.15≥ 2.12.0 and < 2.12.6	Vulnerable	NIST National Vulnerability Database
Nats-io	Nats-server	version < 2.11.15version >= 2.12.0-RC.1, < 2.12.6	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

Low

Privileges required

Low

User interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

Low

Availability

None

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
6.4	CVSS 3.1	Medium	3.1	2.7	security-advisories@github.com via NIST National Vulnerability Database
6.4	CVSS 3.1	Medium	—	—	GitHub_M via CVE Program (cve.org) e CISA ADP
5.4	CVSS 3.1	Medium	2.8	2.5	nvd@nist.gov via NIST National Vulnerability Database

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N (score shown at the top: nvd@nist.gov)

Scoring entities (NIST, CNA, ADP) score independently; each score is shown with its origin. For prioritization we use 6.4 (security-advisories@github.com via NIST National Vulnerability Database) as a conservative provisional reference — not a definitive official score.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-287 · Improper Authentication

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.24%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Review authentication logs: logins without MFA, anomalous sessions and recently created accounts.

web/proxy/WAF logsnetwork IDS/IPSauthentication logs

Timeline

What happened to this CVE, newest first.

2026
Affected products added · nats-io/nats-server
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 13, 2026
CVSS changed · 5.4
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Analyzed
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
Mar 25, 2026 · GitHub_M

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

2 on the record

github.com/nats-io/nats-server/security/advisories/GHSA-55h8-8g96-x4hj
Vendor Advisory, x_refsource_CONFIRM, NIST National Vulnerability Database
advisories.nats.io/CVE/secnote-2026-08.txt
Vendor Advisory, x_refsource_MISC, NIST National Vulnerability Database

Elsewhere on this site

Linuxfoundation
every CVE for this vendor

Authentication
same class

CWE-287
other pages naming this weakness

Related CVEs (same products)

Medium CVE-2026-58211 NATS Server: `no_auth_user` pre-CONNECT fast path bypasses user connection restrictions Jul 8, 2026
High CVE-2026-58208 NATS Server: MQTT-over-WebSocket Path Can Crash WebSocket-Only JetStream Servers Before MQTT Is Enabled Jul 8, 2026
Medium CVE-2026-58207 NATS Server: Remote crash via integer overflow in Connz pagination Jul 8, 2026
Medium CVE-2026-58254 NATS Server: Incomplete fix for CVE-2026-33249: Leaf node connections bypass Nats-Trace-Dest permission check Jul 8, 2026
Medium CVE-2026-58214 NATS Server: MQTT subscribe ACL bypass via $MQTT.deliver.pubrel prefix (incomplete fix for CVE-2026-33217) Jul 8, 2026
High CVE-2026-58250 NATS Server: Pre-auth server crash via double INFO in leafnode handshake Jul 8, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No fixed version, patch or mitigation documented.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-33246 is "NATS: Leafnode connections allow spoofing of Nats-Request-Info identity headers", rated Medium. It affects Nats-server (Linuxfoundation); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.4 describes technical severity. EPSS 0.24% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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