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CVE-2026-33246

NATS: Leafnode connections allow spoofing of Nats-Request-Info identity headers

MEDIUM
5.4
CVSS Score
Published: March 25, 2026 at 07:50 PM UTC
Updated: June 17, 2026 at 10:37 AM UTC
2 products affected across 2 vendorsNats ServerNats Server

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Severity
MEDIUM5.4
Exploit prediction
EPSS 0.1%
SSVC
No known exploit

Description

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Nats Server· Linuxfoundation
95%
v < 2.11.152.12.0 ≤ v < 2.12.6
Nats Server· Nats Io
60%
v < 2.11.15v < 2.12.6
Affected range stops below 2.11.15, so it looks safe — our inference, not a vendor statement
Affected range stops below 2.12.6, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (2)

x_refsource_CONFIRMVendor Advisory
Source: cverecord
https://github.com/nats-io/nats-server/security/advisories/GHSA-55h8-8g96-x4hj
x_refsource_MISCVendor Advisory
Source: cverecord
https://advisories.nats.io/CVE/secnote-2026-08.txt

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

5.4MEDIUM[email protected]
Attack Vector
NETWORK
Complexity
LOW
Privileges
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
LOW
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusANALYZED
CWE
CWE-287CWE-290

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