The vulnerability identified as CVE-2025-56234 affects the AT_NA2000 programmable logic controller (PLC) produced by Nanda Automation Technology. It is a denial-of-service (DoS) vulnerability stemming from the device's TCP stack implementation, specifically how it processes TCP reset (RST) packets. According to RFC 5961, a TCP RST packet should only be accepted if its sequence number exactly matches the next expected sequence number, preventing attackers from easily resetting connections. However, the AT_NA2000 PLC accepts RST packets with sequence numbers anywhere within the current receive window, a much broader range. This flaw allows an attacker to send multiple random TCP RST packets with sequence numbers that fall within this range, causing the PLC to prematurely terminate legitimate TCP connections. The result is a denial-of-service condition where normal communication with the PLC is interrupted, potentially halting industrial processes controlled by the device. The vulnerability does not require any authentication or user interaction, and the attack can be launched remotely over the network. The CVSS v3.1 base score is 7.5, reflecting high severity due to the ease of exploitation and the impact on availability. No patches or vendor advisories are currently available, and no known exploits have been reported in the wild. The vulnerability is categorized under CWE-400 (Uncontrolled Resource Consumption), indicating that the attack can exhaust system resources by repeatedly resetting connections. This issue is particularly critical in industrial environments where AT_NA2000 PLCs are deployed, as disruption can lead to operational downtime and safety risks.

For European organizations, especially those in manufacturing, energy, utilities, and critical infrastructure sectors that deploy AT_NA2000 PLCs, this vulnerability poses a significant operational risk. Successful exploitation can interrupt communication between control systems and PLCs, leading to process halts, production downtime, and potential safety hazards. The denial-of-service condition could affect industrial automation networks, causing cascading failures or delays in critical operations. Given the remote exploitability without authentication, attackers could disrupt operations from outside the network perimeter if adequate protections are not in place. This could also impact supply chains reliant on automated processes controlled by these PLCs. The lack of patches increases the urgency for organizations to implement compensating controls. Additionally, regulatory compliance frameworks in Europe, such as NIS2, emphasize the protection of critical infrastructure, making mitigation of such vulnerabilities a priority to avoid legal and reputational consequences.

Since no patches or firmware updates are currently available from Nanda Automation Technology, European organizations should implement the following specific mitigations: 1) Deploy network segmentation to isolate AT_NA2000 PLCs from general IT networks and restrict access to trusted management stations only. 2) Implement strict firewall rules and intrusion prevention systems (IPS) to detect and block suspicious TCP RST packets, especially those with sequence numbers that could exploit this vulnerability. 3) Use deep packet inspection (DPI) tools capable of enforcing RFC 5961-compliant TCP behavior to prevent acceptance of out-of-sequence RST packets. 4) Monitor network traffic for abnormal TCP reset activity targeting PLC IP addresses and set up alerts for potential exploitation attempts. 5) Employ VPNs or secure tunnels for remote access to PLCs to reduce exposure to external attackers. 6) Engage with the vendor for updates and subscribe to security advisories to apply patches promptly once available. 7) Conduct regular security audits and penetration tests focusing on industrial control system networks to identify and remediate similar protocol handling weaknesses. 8) Train operational technology (OT) personnel to recognize signs of denial-of-service attacks and respond swiftly to minimize downtime.