CVE-2026-33219Network attack vector

Pre-auth service interruption via unbounded WebSocket memory

Published Mar 25, 2026 · Updated Mar 25, 2026

Resource exhaustion in NATS.io NATS Server before 2.11.15 and 2.12.0-RC.1 through 2.12.5 allows remote attackers to interrupt service. The WebSockets client service accepts pre-authentication data without bounding the memory retained while processing it, so memory use grows with bytes supplied. The listener must be enabled and reachable; exploitation needs no credentials but requires sustained, significant client bandwidth and affects availability only.

CVSS severity5.3
Medium
EPSS probability0.53%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in NATS.io NATS Server before 2.11.15 and 2.12.0-RC.1 through 2.12.5 allows remote attackers to interrupt service. The WebSockets client service accepts pre-authentication data without bounding the memory retained while processing it, so memory use grows with bytes supplied. The listener must be enabled and reachable; exploitation needs no credentials but requires sustained, significant client bandwidth and affects availability only.

The record

CVE
CVE-2026-33219
Published
Mar 25, 2026
Updated
Mar 25, 2026
Vendor
NATS.io
Product
NATS Server
Classifications
CWE-770, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 25, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 25, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 2.11.15
  2. Affected versionversion=>= 2.12.0-RC.1, < 2.12.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

NATS.io · NATS Serverversion=< 2.11.15; version=>= 2.12.0-RC.1, < 2.12.6

Published CVSS scores

7.5Red HatCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.3GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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