NATSServer WebSocket Memory Exhaustion before Auth (2.11.15/2.12.6)
CVE-2026-33219 Published on March 25, 2026

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.

NVD

Vulnerability Analysis

CVE-2026-33219 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.

Attack Vector:
NETWORK
Attack Complexity:
LOW
Privileges Required:
NONE
User Interaction:
NONE
Scope:
UNCHANGED
Confidentiality Impact:
NONE
Integrity Impact:
NONE
Availability Impact:
HIGH

Weakness Type

Allocation of Resources Without Limits or Throttling

The software allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor.


Products Associated with CVE-2026-33219

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Red Hat Multicluster Globalhub
 
Red Hat Openshift
 

Affected Versions

nats-io nats-server: Red Hat Multicluster Global Hub 1.4.5: Red Hat Multicluster Global Hub 1.5.4: Red Hat Multicluster Global Hub 1.6.2: Red Hat OpenShift Container Platform 4:

Exploit Probability

EPSS
0.34%
Percentile
26.04%

EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.