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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
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

An unauthenticated client reaching the NATS WebSockets service can consume server memory by sending large amounts of data, potentially disrupting messaging availability. The attacker must supply substantial bandwidth, making this less efficient than a compression-bomb attack, but exposed production services remain at meaningful risk.

Executive priority

Prioritize exposed production messaging systems because successful abuse can interrupt dependent applications without credentials. Patch promptly where WebSockets is externally reachable; otherwise disable or restrict the listener. Internal-only deployments merit scheduled remediation after confirming network controls and business criticality.

Technical view

CVE-2026-33219 is a CWE-770 resource-exhaustion flaw in nats-server before authentication. A WebSockets client can trigger unbounded memory growth proportional to supplied data. It affects versions below 2.11.15 and versions from 2.12.0-RC.1 through 2.12.5. CVSS 3.1 is 7.5, reflecting remotely reachable, unauthenticated availability impact without confidentiality or integrity impact.

Likely exposure

Exposure requires an affected nats-server with WebSockets enabled and reachable by an untrusted client. Internet-facing WebSockets listeners are the clearest concern. Deployments without WebSockets, with inaccessible listeners, or running 2.11.15 or 2.12.6 and later are not described as vulnerable by the supplied advisory.

Exploitation context

The supplied record is not listed in KEV and provides no evidence of active exploitation. Exploitation requires sending substantial data to the WebSockets port, so attacker bandwidth constrains impact. This is distinct from CVE-2026-27571 because it is not a compression bomb.

Researcher notes

The flaw is pre-authentication resource exhaustion with memory consumption corresponding to received data. Available evidence supports availability impact only. Testing should remain controlled because validation can exhaust memory and disrupt service. The source bundle does not identify public exploit code, observed attacks, or additional affected products.

Mitigation direction

  • Upgrade nats-server 2.11 deployments to version 2.11.15 or later.
  • Upgrade nats-server 2.12 deployments to version 2.12.6 or later.
  • Disable WebSockets where the service is not operationally required.
  • Restrict WebSockets listener access to trusted networks while upgrades are completed.

Validation and detection

  • Inventory nats-server versions and identify instances below the fixed releases.
  • Confirm whether WebSockets is enabled on each affected instance.
  • Determine whether untrusted networks can reach the configured WebSockets port.
  • After remediation, verify the deployed binary reports a fixed version.
  • Review memory and availability telemetry for unexplained growth linked to WebSockets traffic.
Prepared
Confidence
high
Sources
4

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

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cwe · low confidence lookup

CWE-770: Exact CWE lookup

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cve · low confidence lookup

CVE-2026-33219 mapping review

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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.

CWE-770 · source CWE mapping

Allocation of Resources Without Limits or Throttling

Allocation of Resources Without Limits or Throttling represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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