Subject: nats-server: Message tracing can be redirected to arbitrary subject

NATS-advisory-ID: 2026-15
Aliases: CVE-2026-33249, GHSA-8m2x-3m6q-6w8j
Date: 2026-03-24
Fixed-In: 2.12.6, 2.11.15

Background:

NATS.io is a high performance open source pub-sub distributed communication
technology, built for the cloud, on-premise, IoT, and edge computing.

The nats-server supports telemetry on messages, using the per-message
NATS headers.


Problem Description:

A valid client which uses message tracing headers can indicate that the
trace messages can be sent to an arbitrary valid subject, including
those to which the client does not have publish permission.

The payload is a valid trace message and not chosen by the attacker.


Affected Versions:

 nats-server: any version before v2.12.6 or v2.11.15


Workarounds:

None.


References:

 * This document is canonically:
   <https://advisories.nats.io/CVE/secnote-2026-15.txt>
 * GHSA advisory:
   <https://github.com/nats-io/nats-server/security/advisories/GHSA-8m2x-3m6q-6w8j>
 * MITRE CVE entry:
   <https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-33249>