CVE-2026-33219

MEDIUM
2026-03-24 https://github.com/nats-io/nats-server
5.3
CVSS 3.1
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CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

Lifecycle Timeline

3
Patch Released
Mar 31, 2026 - 21:13 nvd
Patch available
Analysis Generated
Mar 24, 2026 - 22:01 vuln.today
CVE Published
Mar 24, 2026 - 21:46 nvd
MEDIUM 5.3

Tags

Denial Of Service

Description

### 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.

Analysis

NATS.io nats-server WebSockets service is vulnerable to unbounded memory consumption when malicious unauthenticated clients connect and transmit large amounts of data. This denial-of-service vulnerability affects versions before v2.12.6 or v2.11.15 and has a moderate CVSS score of 5.3 (CWE-770: Allocation of Resources Without Limits or Throttling). …

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Remediation

Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Monitor vendor channels for patch availability.

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Priority Score

27
Low Medium High Critical
KEV: 0
EPSS: +0.1
CVSS: +26
POC: 0

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CVE-2026-33219 vulnerability details – vuln.today
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