CVE-2026-33218: Github.com/nats io/nats server/v2 NATS Has Pre-auth Server Panic Vulnerability
HIGHCVE-2026-33218 is a HIGH (CVSS 7.5) nats has pre-auth server panic vulnerability (CWE-20: Improper Input Validation) affecting Github.com/nats io/nats server/v2 libraries in the Go ecosystem. The issue involves nats has pre-auth server panic via leafnode handling. Remediation is available by upgrading affected packages to version 2.11.15, 2.12.6.
CVE-2026-33218 at a Glance
Security Impact
CVSS: 7.5
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
How to Fix CVE-2026-33218
To remediate this vulnerability, upgrade all affected Github.com/nats io/nats server/v2 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
Upgrade github.com/nats-io/nats-server/v2 to 2.11.15Upgrade github.com/nats-io/nats-server/v2 to 2.12.6Upgrade github.com/nats-io/nats-server to Latest secure releaseRun the following command in your project directory to verify that all resolved dependencies use the patched release:
inspect dependencies for github.com/nats-io/nats-server/v2How to Check if You Are Affected
To determine whether your application is affected by CVE-2026-33218, inspect your project dependencies for Github.com/nats io/nats server/v2:
inspect dependencies for github.com/nats-io/nats-server/v2Analyze the terminal output to locate any version of Github.com/nats io/nats server/v2 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.11.15), your application is affected.
Note: Verify declared build manifests and deployed runtime container environments.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-20: Improper Input Validation, where the product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. In Github.com/nats io/nats server/v2, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2026-33218 Affected Github.com/nats io/nats server/v2 Versions
3 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
github.com/nats-io/nats-server/v2
|
Go |
< 2.11.15
|
2.11.15
|
|
github.com/nats-io/nats-server/v2
|
Go |
≥ 2.12.0-RC.1
< 2.12.6
|
2.12.6
|
|
github.com/nats-io/nats-server
|
Go |
|
|
References
Frequently Asked Questions
What is CVE-2026-33218?
Which Github.com/nats io/nats server/v2 versions are affected?
What version fixes CVE-2026-33218?
Is github.com/nats-io/nats-server/v2 affected?
Is github.com/nats-io/nats-server affected?
What is the CVSS score of CVE-2026-33218?
What CWE is associated with CVE-2026-33218?
How can I check Go dependencies for CVE-2026-33218?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-vprv-35vv-q339",
"modified" : "2026-03-27T22:09:48Z",
"published" : "2026-03-24T21:45:29Z",
"aliases" : [ "CVE-2026-33218" ],
"summary" : "NATS has pre-auth server panic via leafnode handling",
"details" : "### Background\n\nNATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing.\n\nThe nats-server allows hub/spoke topologies using \"leafnode\" connections by other nats-servers.\n\n### Problem Description\n\nA client which can connect to the leafnode port can crash the nats-server with a certain malformed message pre-authentication.\n\n### Affected Versions\n\nAny version before v2.12.6 or v2.11.15\n\n### Workarounds\n\n1. Disable leafnode support if not needed.\n2. Restrict network connections to your leafnode port, if plausible without compromising the service offered.\n\n### References\n\n * This document is canonically: <https://advisories.nats.io/CVE/secnote-2026-10.txt>\n * GHSA advisory: <https://github.com/nats-io/nats-server/security/advisories/GHSA-vprv-35vv-q339>\n * MITRE CVE entry: <https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-33218>",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/nats-io/nats-server/v2"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "2.11.15"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/nats-io/nats-server/v2"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "2.12.0-RC.1"
}, {
"fixed" : "2.12.6"
} ]
} ]
}, {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/nats-io/nats-server"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/nats-io/nats-server/security/advisories/GHSA-vprv-35vv-q339"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-33218"
}, {
"type" : "WEB",
"url" : "https://advisories.nats.io/CVE/secnote-2026-10.txt"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/nats-io/nats-server"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-20" ],
"severity" : "HIGH",
"github_reviewed" : true,
"github_reviewed_at" : "2026-03-24T21:45:29Z",
"nvd_published_at" : "2026-03-25T20:16:32Z"
}
}