LiveActive security incident?Get immediate response
CVE Record

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.

HighCVSS 7.5Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

NATS Server can be forced to consume excessive memory before login when its WebSockets service is reachable. This can disrupt messaging availability, but the sources state attacks require sending a corresponding amount of data and significant client bandwidth.

Executive priority

Treat this as a high-priority availability risk for NATS environments using WebSockets. Patch or disable WebSockets promptly where exposed, with urgency highest for internet-facing or partner-facing messaging services.

Technical view

CVE-2026-33219 is a pre-authentication denial-of-service flaw in nats-server WebSockets handling, categorized as CWE-770. A client able to connect to the WebSockets port can drive unbounded memory use before authentication. Fixed versions are 2.11.15 and 2.12.6.

Likely exposure

Exposure is likely where affected nats-server versions run with WebSockets enabled, especially if the WebSockets port is reachable by untrusted clients. Non-WebSocket deployments are less directly exposed based on the provided sources.

Exploitation context

The source bundle does not state active exploitation, and KEV is false. The issue is network reachable, unauthenticated, and availability-impacting, but the advisory notes attacks require significant client bandwidth.

Researcher notes

This is described as a milder variant of CVE-2026-27571, but not a compression bomb. The issue is pre-auth memory exhaustion over WebSockets, so validation should focus on version, WebSockets configuration, and reachability rather than exploit reproduction.

Mitigation direction

  • Upgrade nats-server to 2.11.15 or 2.12.6.
  • Disable WebSockets if not required for the deployment.
  • Review NATS and Red Hat advisories for product-specific guidance.
  • Prioritize externally reachable WebSockets services first.

Validation and detection

  • Inventory nats-server versions across production and edge environments.
  • Confirm whether WebSockets are enabled on each NATS deployment.
  • Check whether the WebSockets port is reachable by untrusted clients.
  • Verify upgraded hosts report 2.11.15, 2.12.6, or later fixed versions.
Prepared
Confidence
high
Sources
5

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-770: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-33219 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
11Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6redhat-SADP
5.3CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L3.91.4GitHub_M

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-33219Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPgithub.com/nats-io/nats-server: NATS-Server: Denial of Service via unbounded memory use in WebSockets
other:Red Hat severity ratingcvssV3_1
  • 2026-03-25T20:01:41.235Z: Reported to Red Hat.
  • 2026-03-25T19:55:28.363Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
nats-ionats-server< 2.11.15, >= 2.12.0-RC.1, < 2.12.6Listed
Weakness

CWE details

CWE-770

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.