Subject: nats-server: credentials via command-line argv exposed to monitoring

NATS-advisory-ID: 2026-14
Aliases: CVE-2026-33247, GHSA-x6g4-f6q3-fqvv
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 provides an optional monitoring port, which provides
access to sensitive data.  The nats-server can take certain
configuration options on the command-line instead of requiring a
configuration file.


Problem Description:

If a nats-server is run with static credentials for all clients provided
via argv (the command-line), then those credentials are visible to any
user who can see the monitoring port, if that too is enabled.

The /debug/vars end-point contains an unredacted copy of argv.


Affected Versions:

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


Workarounds:

The NATS Maintainers are bemused at the concept of someone deploying a
real configuration using --pass to avoid a config file, but also
enabling monitoring.

Configure credentials inside a configuration file instead of via argv.

Do not enable the monitoring port if using secrets in argv.

Best practice remains to not expose the monitoring port to the Internet,
or to untrusted network sources.


References:

 * This document is canonically:
   <https://advisories.nats.io/CVE/secnote-2026-14.txt>
 * GHSA advisory:
   <https://github.com/nats-io/nats-server/security/advisories/GHSA-x6g4-f6q3-fqvv>
 * MITRE CVE entry:
   <https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-33247>