CVE-2025-5514 is a medium-severity vulnerability identified in the Mitsubishi Electric Corporation MELSEC iQ-F Series FX5U-32MT/ES CPU module, specifically affecting the web server function embedded within these industrial control devices. The vulnerability stems from improper handling of length parameter inconsistencies (classified under CWE-130), which allows a remote unauthenticated attacker to send specially crafted HTTP requests that exploit this flaw. By doing so, the attacker can cause a delay in the processing of the web server function, effectively resulting in a denial-of-service (DoS) condition that prevents legitimate users from accessing or utilizing the web server interface. This vulnerability does not impact confidentiality or integrity but affects availability by disrupting normal operations. The CVSS v3.1 base score is 5.3, reflecting a medium severity level, with an attack vector of network (AV:N), no privileges required (PR:N), no user interaction needed (UI:N), and scope unchanged (S:U). The affected versions include firmware 1.060 and later. No known exploits are currently reported in the wild, and no patches have been linked yet. The vulnerability is significant in the context of industrial control systems (ICS) where availability is critical for operational continuity. The improper length parameter handling suggests that the web server function does not correctly validate or sanitize input length fields, leading to resource exhaustion or processing delays when malformed requests are received. This could be leveraged by attackers to disrupt industrial processes remotely without authentication, posing risks to manufacturing or critical infrastructure environments using these PLCs (Programmable Logic Controllers).

For European organizations, particularly those in manufacturing, energy, utilities, and critical infrastructure sectors that deploy Mitsubishi Electric MELSEC iQ-F Series PLCs, this vulnerability poses a risk of operational disruption. The denial-of-service condition could halt or delay automated control processes, leading to production downtime, safety system failures, or cascading effects on supply chains. Since the vulnerability can be exploited remotely without authentication, attackers do not need insider access, increasing the threat surface. Although the vulnerability does not compromise data confidentiality or integrity, the availability impact can have significant financial and safety consequences. European industrial environments often rely on such PLCs for automation and control; thus, unavailability of the web server interface could impede monitoring, configuration, and maintenance activities. Additionally, regulatory frameworks such as NIS2 Directive emphasize the importance of securing critical infrastructure, making mitigation of such vulnerabilities essential to maintain compliance and operational resilience.

Given the lack of an official patch at the time of this report, European organizations should implement compensating controls to mitigate risk. These include: 1) Network segmentation and strict access controls to limit exposure of the MELSEC iQ-F Series web server interface to trusted management networks only, preventing direct internet or broad network access. 2) Deploy Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) capable of detecting and blocking malformed HTTP requests that may exploit length parameter inconsistencies. 3) Monitor network traffic and device logs for unusual spikes or delays in web server response times indicative of exploitation attempts. 4) Establish rate limiting on HTTP requests to the PLC web server to reduce the impact of flooding attacks. 5) Engage with Mitsubishi Electric for firmware updates or patches and plan timely deployment once available. 6) Conduct regular security assessments and penetration testing focused on ICS components to identify and remediate similar vulnerabilities proactively. 7) Train operational technology (OT) personnel to recognize and respond to availability disruptions promptly. These measures, combined with ongoing vigilance, will reduce the likelihood and impact of exploitation.