CVE-2025-41700: CODESYS Project File RCE Vulnerability

CVE-2025-41700 Overview

CVE-2025-41700 is a high-severity insecure deserialization vulnerability affecting CODESYS development systems. An unauthenticated attacker can trick a local user into executing arbitrary code by opening a deliberately manipulated CODESYS project file. The vulnerability exploits improper handling of serialized data within project files, allowing malicious payloads to execute in the user's security context when the project is opened.

This vulnerability is particularly concerning for industrial control system (ICS) environments where CODESYS is widely deployed for programming programmable logic controllers (PLCs) and industrial automation systems.

Critical Impact

Successful exploitation enables arbitrary code execution in the user context, potentially leading to complete system compromise, data theft, or lateral movement within industrial networks.

Affected Products

• CODESYS Development System (specific versions to be confirmed via vendor advisory)
• Industrial automation environments utilizing CODESYS project files
• Systems where users may open untrusted .project files

Discovery Timeline

• 2025-12-01 - CVE-2025-41700 published to NVD
• 2025-12-01 - Last updated in NVD database

Technical Details for CVE-2025-41700

Vulnerability Analysis

This vulnerability is classified under CWE-502 (Deserialization of Untrusted Data). The CODESYS development system fails to properly validate serialized objects contained within project files before deserializing them. When a user opens a maliciously crafted project file, the embedded payload is automatically deserialized and executed without proper security checks.

The vulnerability has been assigned a CVSS 3.1 base score of 7.8 (High severity) with the following vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Key CVSS metrics indicate:

• Attack Vector (AV:L): Local access required - attacker must deliver malicious file to victim
• Attack Complexity (AC:L): Low complexity - exploitation is straightforward once file is opened
• Privileges Required (PR:N): No prior privileges needed
• User Interaction (UI:R): User must open the malicious project file
• Impact: High confidentiality, integrity, and availability impact

The EPSS (Exploit Prediction Scoring System) indicates a probability of 0.023% with a percentile ranking of 5.319 as of 2025-12-16, suggesting relatively low current exploitation activity.

Root Cause

The root cause lies in insecure deserialization practices within the CODESYS project file parser. The development system does not implement sufficient validation of serialized object types and contents before reconstituting them in memory. This allows attackers to embed arbitrary objects that, when deserialized, trigger code execution through gadget chains or direct payload execution.

The vulnerability occurs because:

1. Project files contain serialized configuration and code objects
2. The parser trusts the integrity of these serialized structures
3. No cryptographic validation or type whitelisting is enforced during deserialization
4. Malicious objects can leverage existing application classes to achieve code execution

Attack Vector

The attack follows a social engineering approach combined with technical exploitation:

1. Preparation: Attacker crafts a malicious CODESYS project file containing a serialized payload designed to execute arbitrary code upon deserialization
2. Delivery: The malicious project file is delivered to the victim via email attachment, file share, compromised repository, or other distribution channels
3. Execution: When the victim opens the project file in their CODESYS development environment, the deserialization process triggers automatic execution of the embedded payload
4. Compromise: The malicious code executes with the privileges of the user running the CODESYS application, potentially enabling system access, data exfiltration, or further attacks on connected industrial systems

The attack requires user interaction (opening the file) but no authentication or special privileges on the attacker's part. Given CODESYS's prevalence in ICS/SCADA environments, successful exploitation could impact critical infrastructure operations.

Detection Methods for CVE-2025-41700

Indicators of Compromise

• Unexpected process spawning from CODESYS development system executables
• Anomalous network connections initiated by CODESYS processes
• Unusual file system activity in user profile directories after opening project files
• Memory artifacts consistent with deserialization attacks
• Presence of unfamiliar or suspicious CODESYS project files (.project extensions)

Detection Strategies

File-Based Detection:
Organizations should implement file scanning for CODESYS project files that exhibit characteristics of deserialization payloads. Security solutions can analyze project file structures for anomalous serialized objects or known malicious patterns.

Behavioral Analysis:
Monitor CODESYS process behavior for signs of exploitation:

• Child process creation from the CODESYS development environment
• Attempts to access sensitive system resources or registry keys
• Network connections to external addresses from development workstations
• Execution of scripting engines (PowerShell, cmd.exe) spawned by CODESYS

Endpoint Detection:
SentinelOne's behavioral AI engine provides autonomous detection of post-exploitation activities resulting from this vulnerability. The Singularity platform monitors for:

• Anomalous code execution patterns originating from legitimate applications
• Deserialization attack indicators across process memory
• Lateral movement attempts following initial compromise

Monitoring Recommendations

Implement comprehensive logging for development workstations running CODESYS:

• Enable Windows process creation auditing (Event ID 4688)
• Monitor file access events for project file directories
• Establish baseline behavior for CODESYS processes and alert on deviations
• Deploy network segmentation monitoring between development environments and production ICS networks

How to Mitigate CVE-2025-41700

Immediate Actions Required

• Review and apply vendor security patches as they become available from CODESYS
• Implement strict policies against opening project files from untrusted or unknown sources
• Enable application whitelisting to prevent unauthorized code execution
• Isolate CODESYS development workstations from sensitive network segments
• Backup critical project files and verify their integrity before use

Patch Information

Refer to the official vendor security advisory at VDE-2025-101 for detailed patching instructions and affected version information. Organizations should coordinate with their CODESYS vendors to obtain and apply security updates addressing this deserialization vulnerability.

Workarounds

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

File Source Verification:
Establish procedures to verify the source and integrity of all CODESYS project files before opening. Consider implementing digital signatures for project files within your organization.

Network Segmentation:
Ensure CODESYS development environments are properly segmented from production ICS/SCADA networks to limit the impact of potential compromise.

User Awareness:
Train engineering staff to recognize social engineering attempts and exercise caution when receiving project files via email or external channels.

Endpoint Protection:
Deploy SentinelOne Singularity on development workstations to provide real-time protection against exploitation attempts and autonomous remediation of threats.