CVE-2026-1876 Overview
CVE-2026-1876 is an Improper Resource Shutdown or Release vulnerability (CWE-404) affecting Mitsubishi Electric Corporation's MELSEC iQ-F Series FX5-ENET/IP Ethernet Module. This Industrial Control System (ICS) vulnerability allows a remote attacker to cause a denial-of-service (DoS) condition by continuously sending UDP packets to the affected products. Recovery requires a complete system reset of the impacted device.
Critical Impact
Remote attackers can disrupt industrial operations by rendering the Ethernet module unresponsive through a sustained UDP packet flood, requiring physical intervention for system recovery.
Affected Products
- Mitsubishi Electric MELSEC iQ-F Series FX5-ENET/IP Ethernet Module (all versions)
Discovery Timeline
- 2026-03-03 - CVE-2026-1876 published to NVD
- 2026-03-04 - Last updated in NVD database
Technical Details for CVE-2026-1876
Vulnerability Analysis
This vulnerability stems from improper resource management within the FX5-ENET/IP Ethernet module's UDP packet handling mechanism. When the device receives a continuous stream of UDP packets, it fails to properly release or manage the associated resources, eventually leading to resource exhaustion and system unresponsiveness.
The attack can be executed remotely over the network without requiring authentication or user interaction. The impact is limited to availability—there is no compromise of data confidentiality or integrity. However, in industrial environments where these programmable logic controllers (PLCs) manage critical manufacturing or infrastructure processes, even temporary unavailability can have significant operational and safety implications.
The MELSEC iQ-F Series is commonly deployed in factory automation, process control, and building management systems, making this vulnerability particularly concerning for operational technology (OT) environments.
Root Cause
The root cause is classified as CWE-404 (Improper Resource Shutdown or Release). The FX5-ENET/IP module does not adequately manage system resources when processing incoming UDP traffic. Under sustained load conditions, the module fails to properly release resources associated with processed packets, leading to progressive resource depletion until the device becomes unresponsive.
Attack Vector
The attack exploits the network-accessible UDP services on the FX5-ENET/IP module. An attacker positioned on the same network segment—or with network access to the ICS environment—can flood the device with UDP packets. The attack requires:
- Network connectivity to the target device
- No authentication or special privileges
- No user interaction
- Sustained packet transmission to exhaust resources
The attack results in complete loss of availability, requiring manual system reset for recovery. This characteristic makes it particularly disruptive in environments where physical access to devices may be limited or where downtime impacts production schedules.
Detection Methods for CVE-2026-1876
Indicators of Compromise
- Unusual volume of UDP traffic directed at FX5-ENET/IP modules
- FX5-ENET/IP modules becoming unresponsive to legitimate communications
- Unexpected system resets or manual recovery operations on affected devices
- Network monitoring alerts indicating UDP flood patterns targeting ICS devices
Detection Strategies
- Implement network traffic analysis to identify anomalous UDP packet volumes targeting ICS assets
- Configure IDS/IPS rules to detect UDP flood patterns against known FX5-ENET/IP device addresses
- Deploy industrial protocol-aware monitoring solutions that can distinguish legitimate automation traffic from attack patterns
- Establish baseline network behavior for ICS segments and alert on deviations
Monitoring Recommendations
- Enable logging on network infrastructure devices to capture traffic patterns to ICS segments
- Monitor FX5-ENET/IP module availability through regular health checks and SNMP polling
- Implement real-time alerting for device unresponsiveness or communication failures
- Correlate ICS network events with security information and event management (SIEM) systems
How to Mitigate CVE-2026-1876
Immediate Actions Required
- Segment ICS networks from corporate and external networks using firewalls and DMZ architectures
- Implement strict access control lists (ACLs) limiting UDP traffic to FX5-ENET/IP modules
- Deploy rate limiting on network devices to prevent UDP flood attacks from reaching ICS assets
- Review and restrict network access to only authorized devices and personnel
Patch Information
Consult the official Mitsubishi Electric Vulnerability Document for the latest patch and firmware update information. Additional guidance is available through the CISA ICS Advisory ICSA-26-62-01 and the JVN Vulnerability Report.
Workarounds
- Implement network segmentation to isolate ICS devices from untrusted networks
- Deploy firewall rules to filter and rate-limit UDP traffic to affected devices
- Use VPN connections for remote access to ICS networks rather than direct exposure
- Consider deploying industrial-grade network monitoring and intrusion prevention systems
# Example firewall rate limiting configuration (iptables)
# Limit UDP packets to ICS device IP to 100 per second
iptables -A INPUT -p udp -d <FX5_ENET_IP> -m limit --limit 100/sec --limit-burst 200 -j ACCEPT
iptables -A INPUT -p udp -d <FX5_ENET_IP> -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
