CVE-2026-1876 is a vulnerability classified under CWE-404 (Improper Resource Shutdown or Release) found in all versions of the Mitsubishi Electric MELSEC iQ-F Series FX5-ENET/IP Ethernet Module. This module is used in industrial automation systems to provide Ethernet/IP connectivity for programmable logic controllers (PLCs). The vulnerability allows a remote attacker to cause a denial-of-service (DoS) condition by continuously sending UDP packets to the device. The improper handling of these packets leads to resource exhaustion or improper shutdown of internal processes, ultimately causing the device to become unresponsive and requiring a manual system reset to restore functionality. The CVSS 4.0 base score is 8.7, indicating high severity, with an attack vector of network (AV:N), no required privileges (PR:N), no user interaction (UI:N), and a high impact on availability (VA:H). The vulnerability does not impact confidentiality or integrity but severely affects availability, which is critical in industrial control environments. No patches or fixes have been published yet, and no known exploits have been reported in the wild. The vulnerability’s exploitation is straightforward due to the lack of authentication or user interaction requirements, making it a significant threat to operational continuity in affected environments.

The primary impact of CVE-2026-1876 is a denial-of-service condition on the MELSEC iQ-F Series FX5-ENET/IP Ethernet Module, which can disrupt industrial automation processes relying on these devices. This can lead to operational downtime, loss of productivity, and potential safety risks in manufacturing plants, critical infrastructure, and other industrial environments. Since the device requires a system reset to recover, prolonged outages may occur if the attack is sustained or if manual intervention is delayed. The vulnerability affects all versions of the product, increasing the scope of risk. Organizations with large-scale deployments of Mitsubishi Electric automation equipment may face significant operational and financial impacts. Additionally, disruption in critical infrastructure sectors such as energy, transportation, and manufacturing could have broader societal and economic consequences. The lack of authentication and ease of exploitation increase the likelihood of opportunistic attacks, especially in environments with exposed or poorly segmented industrial networks.

1. Implement strict network segmentation to isolate MELSEC iQ-F Series FX5-ENET/IP modules from untrusted networks, limiting exposure to potential attackers. 2. Deploy firewall rules or access control lists (ACLs) to block or rate-limit unsolicited UDP traffic directed at these devices, especially from external or less trusted internal sources. 3. Monitor network traffic for unusual spikes in UDP packets targeting the Ethernet modules to detect potential attack attempts early. 4. Establish incident response procedures to quickly identify and reset affected devices to minimize downtime. 5. Coordinate with Mitsubishi Electric for updates or patches and apply them promptly once available. 6. Consider deploying intrusion detection/prevention systems (IDS/IPS) tuned to detect anomalous UDP floods targeting industrial control devices. 7. Conduct regular security assessments and penetration testing focused on industrial control system networks to identify and remediate exposure points. 8. Train operational technology (OT) personnel on recognizing and responding to DoS conditions caused by network-based attacks.