NATS is vulnerable to MQTT hijacking via Client ID (CVE-2026-33215) | HOL Guard CVE

Medium · CVSS 6.5CVE-2026-33215GHSA-FCJP-H8CC-6879

NATS is vulnerable to MQTT hijacking via Client ID

Answer in brief

CVE-2026-33215 records a Medium severity (CVSS 6.5) vulnerability in NATS is vulnerable to MQTT hijacking via Client ID. The current sources do not mark it as known exploited. The current feed maps github.com/nats-io/nats-server/v2 (go), github.com/nats-io/nats-server/v2 (go). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Mar 24, 2026Updated Sep 10, 2026Source checked Sep 10, 2026First seen by HOL Sep 10, 2026Material review Sep 10, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 6.5
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 6.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps github.com/nats-io/nats-server/v2 (go), github.com/nats-io/nats-server/v2 (go). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
github.com/nats-io/nats-server/v2go	>=0 <2.11.15	2.11.15
github.com/nats-io/nats-server/v2go	>=2.12.0-RC.1 <2.12.6	2.12.6

Recommended response

Check inventory. Check lockfiles and deployed manifests for github.com/nats-io/nats-server/v2, github.com/nats-io/nats-server/v2.
Review the reported fix. Update github.com/nats-io/nats-server/v2 to 2.11.15; github.com/nats-io/nats-server/v2 to 2.12.6 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Mar 24, 2026
Evidence: source:osv:source_dates:source-dates:record
Source modified
Sep 10, 2026
Evidence: source:osv:source_dates:source-dates:record
First seen by HOL
Sep 10, 2026

Sources and claim methodology

Upstream source description

### 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>

Quoted source text, attributed separately from HOL analysis.