CVE-2025-41700: Codesys RCE Vulnerability via Project File

CVE-2025-41700 Overview

CVE-2025-41700 affects the CODESYS development system, allowing attackers to execute arbitrary code when a local user opens a manipulated project file. The vulnerability stems from insecure deserialization [CWE-502] of untrusted data within project files. An unauthenticated attacker crafts a malicious CODESYS project and delivers it to a victim through phishing, file shares, or other social engineering channels. When the victim opens the file in the CODESYS development environment, embedded code executes in the user context.

Critical Impact
Successful exploitation grants arbitrary code execution in the context of the engineering workstation user, enabling lateral movement into operational technology (OT) environments and manipulation of industrial control system (ICS) logic.

Affected Products

CODESYS development system (all versions prior to the vendor-supplied fix)
Engineering workstations used to author programmable logic controller (PLC) logic
OT environments where engineers handle externally sourced CODESYS project files

Discovery Timeline

2025-12-01 - CVE-2025-41700 published to the National Vulnerability Database (NVD)
2026-02-23 - Last updated in NVD database

Technical Details for CVE-2025-41700

Vulnerability Analysis

The vulnerability resides in how the CODESYS development system processes project files supplied by external parties. CODESYS project files contain serialized objects and metadata that the integrated development environment (IDE) reconstructs at load time. The deserialization path does not sufficiently validate the contents before instantiating objects or invoking handlers. This permits an attacker to embed malicious payloads that the IDE executes during normal project loading. The resulting code runs with the privileges of the logged-in user, typically an automation engineer with broad access to OT assets.

Root Cause

The root cause is deserialization of untrusted data [CWE-502]. The IDE trusts the structure and content of incoming project files and does not enforce strict type whitelisting or integrity checks. Attackers leverage this trust boundary failure to deliver executable payloads embedded within otherwise legitimate-looking project archives.

Attack Vector

Exploitation requires local file processing and user interaction. An attacker sends a manipulated project file to a CODESYS engineer through email, removable media, or a compromised file share. The engineer opens the file in the CODESYS IDE, triggering deserialization and code execution. No prior authentication to the target workstation is required. Refer to the CERT-VDE Security Advisory for vendor-supplied technical details.

Detection Methods for CVE-2025-41700

Indicators of Compromise

Unexpected child processes spawned by the CODESYS IDE executable shortly after a project file is opened
CODESYS project files received from external or untrusted senders, especially via email attachments
Outbound network connections initiated by the CODESYS IDE process to non-vendor infrastructure
New persistence artifacts (scheduled tasks, registry Run keys) created during or immediately after project loading

Detection Strategies

Monitor process creation events where the CODESYS IDE is the parent process and the child is a shell, scripting engine, or LOLBin
Hunt for file write events from the IDE process targeting startup folders or autorun registry locations
Inspect engineering workstation telemetry for anomalous module loads during project file open operations

Monitoring Recommendations

Apply behavioral analytics to engineering workstations and treat them as high-value assets equivalent to domain controllers
Forward IDE process telemetry, file access logs, and network connections to a centralized data lake for correlation
Establish a baseline of legitimate CODESYS project sources and alert on files originating outside that baseline

How to Mitigate CVE-2025-41700

Immediate Actions Required

Apply the patch referenced in the CERT-VDE Security Advisory VDE-2025-101 to all CODESYS development system installations
Instruct engineers to refuse CODESYS project files from untrusted or unverified sources
Restrict engineering workstation user accounts to least privilege and remove local administrator rights where feasible
Isolate engineering workstations from general-purpose corporate networks and the internet

Patch Information

CODESYS has published a fixed version through CERT-VDE. Review the CERT-VDE Security Advisory for specific version numbers and upgrade guidance. Apply the update to every workstation running the CODESYS development system.

Workarounds

Open untrusted CODESYS project files only inside an isolated virtual machine or sandbox without network access to OT assets
Validate the source and integrity of every project file via checksums or digital signatures before opening
Disable automatic project loading and require explicit user confirmation for files from external locations
Use application allowlisting to prevent the CODESYS IDE from spawning shells, scripting hosts, or other unexpected child processes

bash

# Example: restrict CODESYS IDE child processes via Windows Defender Application Control or AppLocker
# Block common LOLBins from being launched by the CODESYS executable
New-AppLockerPolicy -RuleType Path -User Everyone `
  -Action Deny `
  -Path "%SystemRoot%\System32\cmd.exe","%SystemRoot%\System32\WindowsPowerShell\v1.0\powershell.exe" `
  -Condition "ParentProcess=CODESYS.exe"