CVE-2026-33218Network attack vector

Unauthenticated server crash via pre-CONNECT loop error

Published Mar 25, 2026 · Updated Mar 25, 2026

Denial of service in NATS Server before 2.11.15 and 2.12.0-RC.1 through 2.12.5 allows remote attackers to crash the server. The leafnode connection handler accepts a loop-detection error before any CONNECT message and enters a panic path instead of rejecting the malformed protocol sequence. The leafnode listener must be enabled and network-reachable; no authentication or user interaction is required, and the bounded consequence is a server-process crash.

CVSS severity7.5
High
EPSS probability0.62%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Denial of service in NATS Server before 2.11.15 and 2.12.0-RC.1 through 2.12.5 allows remote attackers to crash the server. The leafnode connection handler accepts a loop-detection error before any CONNECT message and enters a panic path instead of rejecting the malformed protocol sequence. The leafnode listener must be enabled and network-reachable; no authentication or user interaction is required, and the bounded consequence is a server-process crash.

The record

CVE
CVE-2026-33218
Published
Mar 25, 2026
Updated
Mar 25, 2026
Vendor
NATS.io
Product
NATS Server
Classifications
CWE-20, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 25, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 25, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

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

7.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
T1499.004Application or System Exploitation

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo