CVE-2025-41738: CODESYS Control Runtime DoS Vulnerability

CVE-2025-41738 Overview

CVE-2025-41738 is a high-severity type confusion vulnerability affecting the CODESYS Control runtime system's visualisation server. An unauthenticated remote attacker may cause the visualisation server to access a resource with a pointer of the wrong type, potentially leading to a denial-of-service (DoS) condition. This vulnerability is classified under CWE-843 (Access of Resource Using Incompatible Type - Type Confusion).

The vulnerability poses significant risk to industrial control systems (ICS) and operational technology (OT) environments that rely on CODESYS Control runtime systems for automation and process control operations.

Critical Impact

Unauthenticated remote attackers can exploit this type confusion vulnerability to crash the CODESYS visualisation server, causing denial of service to critical industrial control systems without requiring any user interaction or authentication.

Affected Products

• CODESYS Control Runtime System (Visualisation Server Component)
• Industrial automation systems utilizing CODESYS Control
• SCADA/HMI systems with CODESYS visualisation functionality

Discovery Timeline

• 2025-12-01 - CVE-2025-41738 published to NVD
• 2025-12-01 - Last updated in NVD database

Technical Details for CVE-2025-41738

Vulnerability Analysis

This vulnerability is a type confusion flaw (CWE-843) in the CODESYS Control runtime system's visualisation server component. Type confusion occurs when a program allocates or initializes a resource such as a pointer, object, or variable using one type, but later accesses that resource using an incompatible type. In this case, the visualisation server improperly handles pointer types when accessing resources.

The vulnerability has been assigned a CVSS v3.1 score of 7.5 (HIGH) with the vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. This scoring reflects:

• Attack Vector (AV:N): Network-accessible, allowing remote exploitation
• Attack Complexity (AC:L): Low complexity required to exploit
• Privileges Required (PR:N): No authentication needed
• User Interaction (UI:N): No user interaction required
• Confidentiality Impact (C:N): No impact on confidentiality
• Integrity Impact (I:N): No impact on integrity
• Availability Impact (A:H): High impact on availability (DoS)

The EPSS (Exploit Prediction Scoring System) probability is 0.109% with a percentile rank of 29.863, indicating a relatively low likelihood of exploitation in the wild at this time.

Root Cause

The root cause of CVE-2025-41738 lies in improper type handling within the CODESYS visualisation server. When processing certain requests, the server accesses a resource using a pointer that has been cast to or interpreted as an incompatible type. This type mismatch leads to undefined behavior when the server attempts to use the incorrectly-typed pointer to access memory or perform operations.

In industrial control system contexts, such type confusion vulnerabilities typically arise from:

• Improper handling of network protocol messages
• Insufficient validation of data structures received from remote clients
• Legacy code that doesn't enforce strict type safety
• Complex object hierarchies with incorrect type casting

Attack Vector

The attack vector for this vulnerability is network-based, requiring no authentication or user interaction. An attacker can remotely target the CODESYS Control runtime system's visualisation server by sending specially crafted network requests that trigger the type confusion condition.

The exploitation scenario involves an attacker sending malformed or unexpected data to the visualisation server that causes the server to misinterpret the type of a pointer or object. When the server subsequently attempts to access the resource using the wrong type, this leads to memory access violations or other undefined behavior that crashes the service.

Given the nature of the vulnerability, successful exploitation would typically involve:

1. Identifying a network-accessible CODESYS Control runtime system
2. Sending crafted packets to the visualisation server component
3. Triggering the type confusion condition through malformed data
4. Causing the server to crash, resulting in denial of service

For technical details on the vulnerability mechanism and exploitation vectors, refer to the CERT@VDE advisory VDE-2025-100.

Detection Methods for CVE-2025-41738

Indicators of Compromise

• Unexpected crashes or restarts of the CODESYS visualisation server process
• Anomalous network traffic patterns targeting CODESYS Control systems
• Error logs indicating memory access violations or segmentation faults in the visualisation server
• Repeated connection attempts from unknown or suspicious IP addresses to CODESYS services

Detection Strategies

Organizations should implement multiple layers of detection to identify potential exploitation attempts:

Network-Based Detection:

• Monitor for unusual traffic patterns to CODESYS Control systems
• Implement deep packet inspection for malformed protocol messages
• Deploy network intrusion detection systems (NIDS) with signatures for CODESYS protocol anomalies
• Track connection rates and source IPs accessing industrial control systems

Host-Based Detection:

• Monitor CODESYS visualisation server process stability and crash events
• Configure crash dump analysis for the visualisation server component
• Track system event logs for application errors related to CODESYS services
• Implement process monitoring to detect unexpected service terminations

SentinelOne Protection:
SentinelOne's Singularity platform provides comprehensive protection against exploitation attempts targeting industrial control systems through behavioral AI detection, process monitoring, and anomaly detection capabilities that can identify and respond to DoS attacks against critical infrastructure components.

Monitoring Recommendations

• Enable comprehensive logging for all CODESYS Control runtime components
• Implement real-time alerting for visualisation server crashes or restarts
• Deploy network monitoring solutions at ICS/OT network boundaries
• Establish baseline network behavior for CODESYS systems to detect anomalies
• Configure SIEM integration for centralized security event correlation
• Monitor for service availability degradation that may indicate ongoing exploitation

How to Mitigate CVE-2025-41738

Immediate Actions Required

• Review the CERT@VDE advisory VDE-2025-100 for vendor-specific guidance and patches
• Implement network segmentation to restrict access to CODESYS Control systems
• Deploy firewall rules to limit network access to the visualisation server to trusted hosts only
• Monitor CODESYS systems for signs of exploitation or service disruption
• Establish incident response procedures for potential DoS attacks on ICS/OT systems

Patch Information

Organizations should consult the official CERT@VDE advisory VDE-2025-100 for detailed patch information and vendor guidance. Apply security updates provided by CODESYS as soon as they become available. Coordinate patching activities with operational requirements to minimize disruption to industrial processes.

Before applying patches to production systems:

• Test patches in a non-production environment
• Schedule maintenance windows during planned downtime
• Have rollback procedures ready in case of issues
• Document all changes for compliance and audit purposes

Workarounds

If immediate patching is not possible, implement the following defensive measures to reduce risk:

Network-Level Controls:
Restrict access to the CODESYS visualisation server to only authorized management workstations and systems. Implement network segmentation following ICS/SCADA security best practices such as the Purdue Model or IEC 62443 guidelines.

Firewall Configuration:
Configure host-based and network firewalls to limit incoming connections to the visualisation server component. Only allow connections from known, trusted IP addresses within the operational network.

Monitoring and Response:
Increase monitoring of CODESYS systems and establish automated alerts for service disruptions. Have incident response procedures ready to quickly restore service in case of successful exploitation.

# Example network segmentation - restrict access to CODESYS services
# Note: Adjust ports and IP ranges based on your environment

# Allow access only from trusted management network
iptables -A INPUT -p tcp --dport 8080 -s 192.168.100.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP

# Log denied connection attempts for monitoring
iptables -A INPUT -p tcp --dport 8080 -j LOG --log-prefix "CODESYS_BLOCKED: "