LiveActive security incident?Get immediate response
CVE Record

CVE-2026-33217: NATS allows MQTT clients to bypass ACL checks

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, when using ACLs on message subjects, these ACLs were not applied in the `$MQTT.>` namespace, allowing MQTT clients to bypass ACL checks for MQTT subjects. Versions 2.11.15 and 2.12.6 contain a fix. No known workarounds are available.

HighCVSS 8.1Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

NATS Server had an access-control gap affecting MQTT clients. In vulnerable versions, subject ACLs were not enforced in the internal MQTT namespace, so an authenticated MQTT client could reach MQTT subjects it should not access. The vendor fixed this in 2.11.15 and 2.12.6, and no workaround is named in the sources.

Executive priority

Treat as high priority for NATS environments using MQTT and ACLs. It can undermine message confidentiality and integrity without needing admin privileges. Patch affected systems promptly, with urgency highest for internet-reachable or shared messaging infrastructure.

Technical view

Before nats-server 2.11.15 and 2.12.6, ACL checks for message subjects were not applied under the $MQTT.> namespace. The issue is classified as CWE-425 and CWE-863, with CVSS 3.1 score 8.1: network reachable, low complexity, low privileges required, no user interaction, high confidentiality and integrity impact.

Likely exposure

Exposure is most likely where nats-server is below 2.11.15, or in the 2.12.0-RC.1 through pre-2.12.6 range, and MQTT clients are enabled with subject ACLs relied on for access control. Red Hat-packaged deployments should also check listed RHSA advisories.

Exploitation context

The bundle does not identify active exploitation, and KEV is false. Exploitation would require network access and low-privileged credentials. The business risk is unauthorized MQTT subject access, potentially exposing or altering messages protected by ACL policy.

Researcher notes

Evidence supports an authorization bypass in MQTT namespace ACL enforcement, not a general unauthenticated takeover. Sources do not provide exploit prevalence or compensating controls. Validate exposure by version range, MQTT enablement, and whether ACL policy is used for MQTT subjects.

Mitigation direction

  • Upgrade nats-server to 2.11.15, 2.12.6, or later.
  • Apply relevant Red Hat security errata for packaged deployments.
  • Prioritize systems that enable MQTT and rely on subject ACLs.
  • Check vendor guidance because sources state no known workaround.
  • Review MQTT account permissions after patching.

Validation and detection

  • Inventory nats-server versions across production and edge environments.
  • Identify deployments with MQTT enabled.
  • Confirm whether subject ACLs protect MQTT message flows.
  • Verify patched versions or vendor errata are installed.
  • Review logs for unexpected MQTT subject access patterns.
Prepared
Confidence
high
Sources
6

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-425: 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
cwe · medium confidence lookup

CWE-863: Authorization and privilege behavior lookup

Authorization weaknesses can support privilege escalation and valid-account review, depending on exploit path. 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-2026-33217 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
8.1 (3.1)
Known Exploited
No
Published

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

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: 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
8.1CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N2.85.2redhat-SADP
7.1CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N2.84.2GitHub_M

Vulnerability scoring details

Base CVSS 3.1 score

8.1High
CVSS 3.1 vector shape for CVE-2026-33217Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

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: Access control bypass via unapplied ACLs in MQTT namespace
other:Red Hat severity ratingcvssV3_1
  • 2026-03-25T20:01:47.815Z: Reported to Red Hat.
  • 2026-03-25T19:43:40.969Z: 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-425CWE-863

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

CWE-425 · source CWE mapping

Direct Request ('Forced Browsing')

Direct Request ('Forced Browsing') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-863 · source CWE mapping

Incorrect Authorization

Incorrect Authorization represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs