NATS is vulnerable to MQTT hijacking via Client ID

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.5 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:L

EPSS

• CVE-2026-33215: 0.24% estimated exploitation activity in the next 30 days; percentile 15.72 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 MQTT client interface. Problem Description Sessions and Messages can by hijacked via MQTT Client ID malfeasance. Affected Versions Any version before v2.12.6 or v2.11.15 Workarounds None. Resources This document is canonically: <https://advisories.nats.io/CVE/secnote-2026-06.txt GHSA advisory: <https://github.com/nats-io/nats-server/security/advisories/GHSA-fcjp-h8cc-6879 MITRE CVE entry: <https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-33215

Published by the source

24 Mar 2026, 21:39 UTC

Last modified by the source

27 Mar 2026, 20:55 UTC

Source last checked

26 Oct 2026, 15:18 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-fcjp-h8cc-6879

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# Patch Next advisory brief: CVE-2026-33215

Advisory: NATS is vulnerable to MQTT hijacking via Client ID
IDs: CVE-2026-33215, GHSA-fcjp-h8cc-6879
Record: https://patchnext.com/advisories/cve-2026-33215 (revision 1, source checked 26 Oct 2026, 15:18 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/nats-io/nats-server/v2 2.12.6, 2.11.15. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/nats-io/nats-server/v2: affected < 2.11.15; >= 2.12.0-RC.1, < 2.12.6; fixed in 2.12.6, 2.11.15

## Suggested inspection (read-only)
- Go github.com/nats-io/nats-server/v2: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/nats-io/nats-server/v2.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-fcjp-h8cc-6879 (GitHub-reviewed advisory GHSA-fcjp-h8cc-6879 lists affected ranges: Go github.com/nats-io/nats-server/v2 >=0 =2.12.0-RC.1 <2.12.6)

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