CVE-2026-33219

NATS is vulnerable to pre-auth DoS through WebSockets client service

CVSS 3.1 5.3 MEDIUMEUVD CVSS 3.1 7.5 CVSS 3.1 · [email protected] · Secondary 5.3 MEDIUMCVSS 3.1 · 0b0ca135-0b70-47e7-9f44-1890c2a1c46c · Secondary 7.5 HIGHCVSS_V3 Publisher rating MODERATEFixed by github.com/nats-io/nats-server/v2 2.11.15 Fixed by github.com/nats-io/nats-server/v2 2.12.6osv · severity unknownFixed by github.com/nats-io/nats-server/v2 2.11.15 Fixed by github.com/nats-io/nats-server/v2 2.12.6KEV status unknown

Original advisory

cve-program · CVE-2026-33219

Published

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, a 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. This is a milder variant of CVE-2026-27571. That earlier issue was a compression bomb, this vulnerability is not. Attacks against this new issue thus require significant client bandwidth. Versions 2.11.15 and 2.12.6 contain a fix. As a workaround, disable websockets if not required for project deployment.

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euvd · EUVD-2026-15970

Published

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nvd · CVE-2026-33219

Published

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osv · GHSA-8r68-gvr4-jh7j

Published

### 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 offers a WebSockets client service, used in deployments where browsers are the NATS clients. ### Problem Description A 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. This 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). That earlier issue was a compression bomb, this vulnerability is not. Attacks against this new issue thus require significant client bandwidth. ### Affected Versions Any version before v2.12.6 or v2.11.15 ### Workarounds Disable websockets if not required for project deployment.

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osv · GO-2026-4831

Published

NATS is vulnerable to pre-auth DoS through WebSockets client service in github.com/nats-io/nats-server

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Affected versions, risk and source history

Exploitation and risk

Source status

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cve-program · CVE-2026-33219

Published

NATS is vulnerable to pre-auth DoS through WebSockets client service

Source published: 25 Mar 2026 19:55:28 UTC
Source modified: 9 Sep 2026 12:05:04 UTC
Saved here: 23 Oct 2026 15:48:27 UTC
Source terms: CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

euvd · EUVD-2026-15970

Published

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, a malicious client which can connect to the WebSockets port can cause unbounded memory use in the nats-ser…

Additional publisher context

EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.

Original publisher date fields

datePublished: Mar 25, 2026, 7:55:28 PM

dateUpdated: Sep 9, 2026, 12:05:04 PM

4 related source bulletins · separate from aliases

RHSA-2026:23345: Red Hat Security Advisory: Multicluster Global Hub 1.6.2 security update

CVE-2026-4427 · CVE-2026-21728 · CVE-2026-25679 · CVE-2026-27137 · CVE-2026-27889 · CVE-2026-29785 · CVE-2026-32280 · CVE-2026-32281 · CVE-2026-32282 · CVE-2026-32283 · CVE-2026-32285 · CVE-2026-32286 · CVE-2026-33186 · CVE-2026-33215 · CVE-2026-33216 · CVE-2026-33217 · CVE-2026-33218 · CVE-2026-33219 · CVE-2026-33247 · CVE-2026-33413 · CVE-2026-33487 · CVE-2026-33810 · CVE-2026-33813 · CVE-2026-33997 · CVE-2026-34040 · CVE-2026-34986 · CVE-2026-40890 · CVE-2026-41602 · CVE-2026-41603 · CVE-2026-41604 · CVE-2026-41605 · CVE-2026-41606 · CVE-2026-41607 · CVE-2026-41636 · CVE-2026-43869

RHSA-2026:22347: Red Hat Security Advisory: Multicluster Global Hub 1.4.5 security update

RHSA-2026:21769: Red Hat Security Advisory: Multicluster Global Hub 1.5.4 security update

WID-SEC-W-2026-0858: NATS Server: Mehrere Schwachstellen

CVE-2026-33215 · CVE-2026-33216 · CVE-2026-33217 · CVE-2026-33218 · CVE-2026-33219 · CVE-2026-33222 · CVE-2026-33223 · CVE-2026-33246 · CVE-2026-33247 · CVE-2026-33248 · CVE-2026-33249

Source published: Mar 25, 2026, 7:55:28 PM (timezone not stated)
Source modified: Sep 9, 2026, 12:05:04 PM (timezone not stated)
Saved here: 15 Nov 2026 09:38:12 UTC
Source terms: ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

Source: euvd · ENISA EUVD · source terms and attribution apply. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

EUVD CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

nvd · CVE-2026-33219

Published

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, a malicious client which can connect to the WebSockets port can cause unbounded memory use in the nats-ser…

Additional publisher context

NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.

Source analysis status: Modified

Weakness classifications: CWE-770

Original publisher date fields

published: 2026-03-25T20:16:32.777

lastModified: 2026-09-09T13:19:24.173

1 source CPE criteria · context only

cpe:2.3:a:linuxfoundation:nats-server:*:*:*:*:*:*:*:*

The original JSON retains the logical configuration operators, exclusions and version bounds.

Source published: 25 Mar 2026 20:16:32 UTC
Source modified: 9 Sep 2026 13:19:24 UTC
Saved here: 25 Oct 2026 08:17:18 UTC
Source terms: NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

Source: nvd · NIST NVD usage terms; underlying source attribution retained. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · [email protected] · Secondary · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS 3.1 · 0b0ca135-0b70-47e7-9f44-1890c2a1c46c · Secondary · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

osv · GHSA-8r68-gvr4-jh7j

Published

NATS is vulnerable to pre-auth DoS through WebSockets client service

Source published: 24 Mar 2026 21:46:31 UTC
Source modified: 10 Sep 2026 03:50:38 UTC
Saved here: 24 Oct 2026 13:19:41 UTC
Source terms: GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Publisher rating · MODERATE

osv · GO-2026-4831

Published

NATS is vulnerable to pre-auth DoS through WebSockets client service in github.com/nats-io/nats-server

Source published: 26 Mar 2026 20:33:05 UTC
Source modified: 27 Mar 2026 18:26:09 UTC
Saved here: 24 Oct 2026 13:19:41 UTC
Source terms: OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

Source: osv · OSV · upstream source license applies. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.