nats-io nats-server up to 2.11.14/2.12.5 Websockets Client Service denial of service

Summaryinfo

A vulnerability was found in nats-io nats-server up to 2.11.14/2.12.5. It has been rated as problematic. Affected is an unknown function of the component Websockets Client Service. Performing a manipulation results in denial of service. This vulnerability is cataloged as CVE-2026-33219. It is possible to initiate the attack remotely. There is no exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability classified as problematic has been found in nats-io nats-server up to 2.11.14/2.12.5. This affects an unknown function of the component Websockets Client Service. The manipulation with an unknown input leads to a denial of service vulnerability. CWE is classifying the issue as CWE-404. The product does not release or incorrectly releases a resource before it is made available for re-use. This is going to have an impact on availability. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-33219. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

The vulnerability scanner Nessus provides a plugin with the ID 303832 (Linux Distros Unpatched Vulnerability : CVE-2026-33219), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 2.11.15 or 2.12.6 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (303832). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Productinfo

Vendor

• nats-io

Name

• nats-server

Version

• 2.11.0
• 2.11.1
• 2.11.2
• 2.11.3
• 2.11.4
• 2.11.5
• 2.11.6
• 2.11.7
• 2.11.8
• 2.11.9
• 2.11.10
• 2.11.11
• 2.11.12
• 2.11.13
• 2.11.14
• 2.12.0
• 2.12.1
• 2.12.2
• 2.12.3
• 2.12.4
• 2.12.5

CPE 2.3info

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CPE 2.2info

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If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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