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CVE Record

CVE-2026-33218: NATS has pre-auth server panic via leafnode handling

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 client which can connect to the leafnode port can crash the nats-server with a certain malformed message pre-authentication. Versions 2.11.15 and 2.12.6 contain a fix. As a workaround, disable leafnode support if not needed or restrict network connections to the leafnode port, if plausible without compromising the service offered.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2026-33218 lets an unauthenticated network client crash NATS Server if it can reach the leafnode port. The impact is service availability: messaging infrastructure can be taken down, but the provided sources do not indicate data theft or modification.

Executive priority

Prioritize remediation for production messaging clusters with reachable leafnode ports. The business risk is service disruption rather than confirmed compromise, but unauthenticated crash conditions in messaging infrastructure can affect dependent applications quickly.

Technical view

NATS Server before 2.11.15 and the 2.12 release-candidate line before 2.12.6 can panic during pre-authentication leafnode message handling. The issue is categorized as CWE-1286 and CWE-20, with CVSS 3.1 score 7.5 for network, low-complexity, unauthenticated availability impact.

Likely exposure

Exposure is likely where nats-server leafnode support is enabled and the leafnode port is reachable by untrusted clients, partners, or the internet. Systems without leafnode enabled, or with tightly restricted leafnode network access, have lower practical exposure based on the provided sources.

Exploitation context

The bundle marks KEV as false and provides no cited evidence of active exploitation. The vulnerability is still operationally serious because it is unauthenticated, network reachable, and can crash the server before authentication if the leafnode port is accessible.

Researcher notes

Do not assume all NATS deployments are exposed; leafnode reachability is the key condition. The public bundle names fixed versions and workaround direction, but does not provide exploit-in-the-wild evidence or broader product impact beyond nats-io nats-server and referenced Red Hat advisories.

Mitigation direction

  • Upgrade nats-server to 2.11.15 or 2.12.6 or later.
  • Disable leafnode support if it is not required.
  • Restrict network access to the leafnode port where service design permits.
  • Apply relevant Red Hat errata for affected packaged deployments.
  • Monitor NATS and vendor advisories for updated guidance.

Validation and detection

  • Inventory all nats-server deployments and record running versions.
  • Confirm whether leafnode support is enabled on each server.
  • Verify which networks can reach the leafnode port.
  • Check package source and vendor errata status for downstream builds.
  • Review logs and uptime history for unexplained nats-server crashes.
Prepared
Confidence
high
Sources
8

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-1286: Exact CWE lookup

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cwe · low confidence lookup

CWE-20: Exact CWE lookup

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Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-33218 mapping review

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

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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
9Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical 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:H3.93.6GitHub_M
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

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-33218Attack 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-SADPnats-server: github.com/nats-io/nats-server: NATS-Server: Denial of Service via malformed message pre-authentication on leafnode port
other:Red Hat severity ratingcvssV3_1
  • 2026-03-25T20:02:13.680Z: Reported to Red Hat.
  • 2026-03-25T19:53:12.075Z: 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-1286CWE-20

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