CVE-2026-22535 identifies a critical vulnerability in EFACEC QC 60/90/120 products, specifically related to the use of the MQTT protocol for device communications. The root cause is the use of unsecured, unencrypted MQTT communications, which allows an attacker who has network access and valid credentials to write arbitrary data to server topics controlling the MQTT communications board. This weakness corresponds to CWE-1366, indicating frail security in protocol implementation. The vulnerability requires an attacker to have low privileges (PR:L) and access to the adjacent network (AV:A), but no user interaction is necessary. The attack complexity is high (AC:H), reflecting some difficulty in exploitation, likely due to the need for credentials and network proximity. The impact is severe across confidentiality, integrity, and availability (all rated high), meaning an attacker could manipulate device behavior, disrupt communications, or exfiltrate sensitive information. The EFACEC QC series is used in industrial control and critical infrastructure environments, where MQTT is commonly employed for lightweight messaging. The lack of encryption in MQTT traffic exposes these systems to interception and manipulation. Although no known exploits are currently in the wild, the vulnerability's publication and high CVSS score indicate a significant risk. The absence of available patches necessitates immediate compensating controls. The vulnerability's presence in version 8 of the product line suggests that organizations running this version are vulnerable until remediation is applied.

For European organizations, especially those operating critical infrastructure, manufacturing, or industrial automation systems using EFACEC QC 60/90/120 devices, this vulnerability poses a substantial risk. Exploitation could lead to unauthorized control over device communications, potentially causing operational disruptions, data manipulation, or leakage of sensitive information. The compromise of MQTT communications could allow attackers to inject malicious commands or disrupt monitoring and control functions, leading to safety hazards or production downtime. Given the high confidentiality, integrity, and availability impacts, affected organizations may face regulatory compliance issues, financial losses, and reputational damage. The requirement for network access and credentials limits exploitation to insiders or attackers who have breached perimeter defenses, but once inside, the threat is significant. The lack of encryption in MQTT traffic also increases the risk of interception and replay attacks, further exacerbating the threat landscape for European entities relying on these devices.

To mitigate CVE-2026-22535, European organizations should implement the following specific measures: 1) Immediately enforce the use of encrypted MQTT communications by configuring MQTT over TLS (MQTTS) to protect data in transit and prevent unauthorized message injection. 2) Strengthen credential management by enforcing strong, unique passwords and rotating credentials regularly to reduce the risk of credential compromise. 3) Segment networks to isolate EFACEC QC devices from general IT networks and restrict MQTT communication to trusted hosts only, minimizing attack surface exposure. 4) Deploy network monitoring and anomaly detection tools focused on MQTT traffic to identify unusual write operations or unauthorized access attempts. 5) Engage with EFACEC for patches or firmware updates addressing this vulnerability and plan timely deployment once available. 6) Conduct regular security audits and penetration tests on industrial control networks to identify and remediate similar protocol weaknesses. 7) Educate operational technology (OT) personnel on secure MQTT configuration and the risks of unsecured communications. These targeted actions go beyond generic advice by focusing on protocol-level encryption, credential hygiene, network architecture, and active monitoring tailored to the vulnerability's specifics.