CVE-2026-33219 | NATS is vulnerable to pre-auth DoS through WebSockets client service

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.

Published: 2026-03-25 Last update: 2026-03-26 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-33219 is rated Low Risk (27.7/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.06%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-33219

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-03-26 — 0.06% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-33219

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:L)
Might cause slowdowns, glitches, or partial disruption—not a full brick.
 3.9 1.4 [email protected]

Weakness enumeration for CVE-2026-33219

GitHub Security Advisory for CVE-2026-33219

GHSA-8r68-gvr4-jh7j · Severity: medium · Ecosystem: go — NATS is vulnerable to pre-auth DoS through WebSockets client service

OS Trackers for CVE-2026-33219

vendor priority summary link
alpine — CVE-2026-33219: 1 source package rows (nats-server); 39 state rows across 2 repos (3.23-community, edge-community); fixed 2, open 37. https://security.alpinelinux.org/vuln/CVE-2026-33219
debian not yet assigned CVE-2026-33219 not yet assigned priority: Debian including 1 source packages (nats-server), 4 status rows across 4 suites (bookworm, forky, sid, trixie): open 2, resolved 2. https://security-tracker.debian.org/tracker/CVE-2026-33219
redhat high — https://access.redhat.com/security/cve/CVE-2026-33219
suse medium — https://www.suse.com/security/cve/CVE-2026-33219/
ubuntu medium CVE-2026-33219 medium priority: Ubuntu including 1 source packages (nats-server), 4 status rows across 4 suites (jammy, noble, questing, upstream): needs-triage 3, DNE 1. https://ubuntu.com/security/CVE-2026-33219

Affected software / configurations for CVE-2026-33219

Vendor Product Version Raw CPE
linuxfoundation nats-server < 2.11.15 cpe:2.3:a:linuxfoundation:nats-server:*:*:*:*:*:*:*:*
linuxfoundation nats-server >= 2.12.0, < 2.12.6 cpe:2.3:a:linuxfoundation:nats-server:*:*:*:*:*:*:*:*

References for CVE-2026-33219

cvelogic Threat Intelligence