CVE-2026-33219: Github.com/nats io/nats server Denial of Service Vulnerability
MODERATECVE-2026-33219 is a MODERATE (CVSS 5.3) denial of service vulnerability (CWE-770: Allocation of Resources Without Limits or Throttling) affecting Github.com/nats io/nats server libraries in the Go ecosystem. The issue involves nats is vulnerable to pre-auth dos through websockets client service. Remediation is available by upgrading affected packages to version 2.11.15, 2.12.6.
CVE-2026-33219 at a Glance
Security Impact
CVSS: 5.3
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:L).
How to Fix CVE-2026-33219
To remediate this vulnerability, upgrade all affected Github.com/nats io/nats server 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 to Latest secure releaseUpgrade github.com/nats-io/nats-server/v2 to 2.11.15Upgrade github.com/nats-io/nats-server/v2 to 2.12.6Run 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-serverHow to Check if You Are Affected
To determine whether your application is affected by CVE-2026-33219, inspect your project dependencies for Github.com/nats io/nats server:
inspect dependencies for github.com/nats-io/nats-serverAnalyze the terminal output to locate any version of Github.com/nats io/nats server 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-770: Allocation of Resources Without Limits or Throttling, where the product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. In Github.com/nats io/nats server, 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-2026-33219 Affected Github.com/nats io/nats server Versions
3 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
github.com/nats-io/nats-server
|
Go |
|
|
|
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
|
References
Frequently Asked Questions
What is CVE-2026-33219?
Which Github.com/nats io/nats server versions are affected?
What version fixes CVE-2026-33219?
Is github.com/nats-io/nats-server affected?
Is github.com/nats-io/nats-server/v2 affected?
What is the CVSS score of CVE-2026-33219?
What CWE is associated with CVE-2026-33219?
How can I check Go dependencies for CVE-2026-33219?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-8r68-gvr4-jh7j",
"modified" : "2026-03-27T22:09:59Z",
"published" : "2026-03-24T21:46:31Z",
"aliases" : [ "CVE-2026-33219" ],
"summary" : "NATS is vulnerable to pre-auth DoS through WebSockets client service",
"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 offers a WebSockets client service, used in deployments where browsers are the NATS clients.\n\n### Problem Description\n\nA malicious client which can connect to the WebSockets port can cause unbounded memory use in the nats-server before authentication; this requires sending a corresponding amount of data.\n\nThis is a milder variant of [NATS-advisory-ID 2026-02](https://advisories.nats.io/CVE/secnote-2026-02.txt) (aka CVE-2026-27571; GHSA-qrvq-68c2-7grw).\nThat earlier issue was a compression bomb, this vulnerability is not. Attacks against this new issue thus require significant client bandwidth.\n\n### Affected Versions\n\nAny version before v2.12.6 or v2.11.15\n\n### Workarounds\n\nDisable websockets if not required for project deployment.",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
} ],
"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-8r68-gvr4-jh7j"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-33219"
}, {
"type" : "WEB",
"url" : "https://advisories.nats.io/CVE/secnote-2026-02.txt"
}, {
"type" : "WEB",
"url" : "https://advisories.nats.io/CVE/secnote-2026-11.txt"
}, {
"type" : "ADVISORY",
"url" : "https://github.com/advisories/GHSA-qrvq-68c2-7grw"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/nats-io/nats-server"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-770" ],
"severity" : "MODERATE",
"github_reviewed" : true,
"github_reviewed_at" : "2026-03-24T21:46:31Z",
"nvd_published_at" : "2026-03-25T20:16:32Z"
}
}