CVE-2026-33215Network attack vector

Unauthenticated MQTT session hijacking via Client ID

Published Mar 24, 2026 · Updated Mar 24, 2026

Improper authentication in NATS Server before 2.11.15 and 2.12.0-RC.1 through 2.12.5 allows remote attackers to hijack MQTT sessions. A crafted MQTT Client ID causes one client to obtain another client's session and messages, but NATS.io has not disclosed the validation or lookup error that permits the takeover. The MQTT interface must be enabled and network-reachable; no authentication or user interaction is required, and the disclosed impact is confined to MQTT sessions and their messages.

CVSS severity6.5
Medium
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authentication in NATS Server before 2.11.15 and 2.12.0-RC.1 through 2.12.5 allows remote attackers to hijack MQTT sessions. A crafted MQTT Client ID causes one client to obtain another client's session and messages, but NATS.io has not disclosed the validation or lookup error that permits the takeover. The MQTT interface must be enabled and network-reachable; no authentication or user interaction is required, and the disclosed impact is confined to MQTT sessions and their messages.

The record

CVE
CVE-2026-33215
Published
Mar 24, 2026
Updated
Mar 24, 2026
Vendor
NATS.io
Product
NATS Server
Classifications
CWE-287, CWE-488, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 24, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 24, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 2.11.15
  2. Affected versionversion=>= 2.12.0-RC.1, < 2.12.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

NATS.io · NATS Serverversion=< 2.11.15; version=>= 2.12.0-RC.1, < 2.12.6

Published CVSS scores

6.5GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:L
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-287Improper Authentication
CWE-488Exposure of Data Element to Wrong Session
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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