CVE-2025-3947 is a high-severity integer underflow vulnerability (CWE-191) identified in Honeywell's Experion PKS control system, specifically affecting the C300 PCNT02 and several related products including C300 PCNT05, FIM4, FIM8, UOC, CN100, HCA, C300PM, and C200E. The vulnerability exists within the Control Data Access (CDA) component of the system. It arises due to improper handling of integer values during subtraction operations, which can cause an integer underflow or wraparound condition. This flaw allows an attacker to manipulate input data in a way that bypasses proper integer value checks, potentially leading to denial of service (DoS) conditions. The CVSS v3.1 base score is 8.2, indicating a high severity level, with an attack vector of network (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), no confidentiality impact (C:N), low integrity impact (I:L), and high availability impact (A:H). The vulnerability affects Honeywell Experion PKS versions from 520.1 through 520.2 TCU9 and from 530 through 530 TCU3. Honeywell recommends upgrading to the latest patched versions 520.2 TCU9 HF1 and 530.1 TCU3 HF1 to remediate this issue. No known exploits are currently reported in the wild. This vulnerability is critical for industrial control systems (ICS) environments where Experion PKS is deployed, as it could disrupt operational continuity by causing system crashes or failures through denial of service.

For European organizations, especially those operating critical infrastructure such as energy, manufacturing, and utilities that rely on Honeywell Experion PKS for process control and automation, this vulnerability poses a significant risk. Exploitation could lead to denial of service, disrupting industrial processes and potentially causing safety hazards or production downtime. The lack of confidentiality impact reduces the risk of data leakage, but the integrity and availability impacts remain concerning. Given the network attack vector and no requirement for privileges or user interaction, remote exploitation is feasible, increasing the threat landscape. Disruption in critical infrastructure could have cascading effects on supply chains and essential services. Additionally, regulatory compliance frameworks in Europe, such as NIS2 Directive and GDPR, may impose strict requirements on managing such vulnerabilities and reporting incidents, increasing the operational and legal impact of exploitation.

European organizations should prioritize immediate assessment of their Honeywell Experion PKS deployments to identify affected versions. Specific mitigation steps include: 1) Applying the vendor-recommended patches by upgrading to Honeywell Experion PKS versions 520.2 TCU9 HF1 or 530.1 TCU3 HF1 without delay. 2) Implement network segmentation to isolate control systems from general IT networks and limit exposure to untrusted networks. 3) Employ strict access controls and monitoring on the Control Data Access (CDA) interfaces to detect anomalous input data patterns that could indicate exploitation attempts. 4) Conduct thorough vulnerability scanning and penetration testing focused on industrial control system components to verify patch effectiveness and identify residual risks. 5) Implement intrusion detection systems (IDS) tailored for ICS environments to detect potential exploitation attempts in real time. 6) Develop and rehearse incident response plans specific to ICS denial of service scenarios to minimize operational impact. 7) Engage with Honeywell support and subscribe to threat intelligence feeds for updates on any emerging exploits or additional mitigations.