CODESYS V3 Flaws in Schneider Electric Gear: Patch Guidance and Mitigations

Schneider Electric has confirmed that a broad family of its products that embed the CODESYS V3 runtime are affected by multiple high‑severity vulnerabilities in the CODESYS communication server — flaws that, left unaddressed, can lead to denial‑of‑service and, in many cases, arbitrary remote code execution on controllers, HMIs and soft‑runtime components used across manufacturing, energy and commercial facilities.

Background / Overview​

CODESYS is a widely deployed IEC‑61131‑3 automation runtime and development stack that third‑party vendors embed in PLCs, HMIs and machine‑control software. Microsoft’s red‑team analysis of the CODESYS V3 SDK uncovered a cluster of memory‑safety and input‑validation flaws (the “CoDe16” family and related CVEs) that affect CODESYS V3 releases prior to 3.5.19.0; those defects are the root cause of the issues Schneider Electric is now addressing in its product lines. Schneider Electric’s public security notification maps the runtime‑level CVEs to product families including Modicon M241 / M251 / M262 / M258 / LMC058 / LMC078 / M218 controllers, PacDrive 3 LMC Eco/Pro controllers, HMISCU and a number of EcoStruxure Machine Expert and Vijeo Designer embedded runtimes. Schneider’s advisory calls out both patch releases and a set of mitigations for devices where a firmware/patch is not available or where the device has reached end‑of‑commercialization. Independent threat researchers and vendors (Microsoft, industry blogs and vulnerability trackers) class the most dangerous of these CODESYS issues as high‑severity buffer‑overflow and out‑of‑bounds write flaws (many carrying CVSS v3 scores in the 7.5–8.8 range) that require authentication to exploit — but that authentication requirement can sometimes be undermined by other weaknesses (legacy defaults, exposed ports, or prior credential exposures), meaning “authenticated” is an important but not absolute mitigation.

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What’s affected — product groups and CVE families​

Schneider’s notification enumerates dozens of CVE identifiers as they map to product lines. The practical micro and machine controllers: M241, M251, M262, M258, M218, LMC058, LMC078 and Easy Modicon M310.

• PacDrive 3 controllers (LMC Eco / Pro / Pro2).
• HMIs and HMI‑embedded runtimes: Harmony (Magelis) HMIGK / HMIGTO / HMIGTU / HMIGTUX / HMISTU, Easy Harmony families, Magelis XBT and HMISCU controllers.
• Soft runtimes and engineering workstations: SoftSPS embedded in EcoStruxure Machine Expert, Vijeo Designer runtime (including Vijeo Designer Basic) and Machine Expert engineering tools.
• Other EcoStruxure components that embed CODESYS for logic execution or remote project transfer.

Key CVE clusters called out in vendor and public advisories include:

• The CoDe16 set (CVE‑2022‑47378 through CVE‑2022‑47393), dominated by buffer overflow / out‑of‑bounds write and improper input validation issues.
• Additional CODESYS‑protocol and runtime integrity gaps such as CVE‑2022‑4046 and CVE‑2023‑28355 (checksum/integrity and memory access functions) that allow PLC code to read or write arbitrary runtime memory under certain conditions.

Practical note: Schneider’s product list marks some SKUs “All Versions” affected (meaning the affected CODESYS runtime is present across all shipped versions), while other SKUs have specific firmware/patch version thresholds for remediation. For some older or discontinued SKUs (for example Magelis XBT, certain LMC and M218 controllers) Schneider recommends migration because fixes are not planned. Customers must consult the vendor advisory and their firmware inventory to determine the exact exposure for each serial number and firmware revision.

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Why these bugs are dangerous (technical summary)​

• Buffer overflows and out‑of‑bounds writes: Several CODESYS components copy tag/packet payloads into fixed‑size buffers without adequately validating lengths. An attacker who can send crafted messages to the affected CODESYS service can overwrite stack or heap memory, causing crashes (DoS) or, in crafted cases, writing attacker data that leads to code execution. The Microsoft analysis explains multiple locations in the protocol stack where tag decoding allows unchecked copying.
• Integrity/checksum bypasses: In some CODESYS setups the mechanism intended to detect modified PLC application code or boot images is insufficient; a compromised PLC application loaded into RAM may not be reliably detected by the development system’s checksum mechanism, enabling persistent tampering. Schneider’s advisory specifically notes weaknesses in project/boot integrity checks.
• Protocol exposure: The CODESYS protocol operates over UDP/TCP (commonly UDP 1740, TCP 11740 and adjacent ports) and uses binary tag structures. When these ports are reachable from untrusted networks or insufficiently segmented enterprise LANs, the attack surface increases dramatically. Microsoft and follow‑on vendors have published network discovery heuristics and open‑source forensics tools to help identify devices using the vulnerable runtime.
• Authentication caveat: Many of the CODESYS CVEs require authentication to trigger, which is a meaningful barrier, but real‑world control systems frequently suffer from weak or default credentials, local access or exposed management ports. Threat actors can combine weaknesses (e.g., default password settings, exposed engineering stations, or other CVEs) to gain the required privileges and then exploit these high‑impact runtime flaws.

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Vendor response and remediation status​

Schneider Electric has published a structured remediation and mitigation roadmap:

• Firmware / software fixes: Schneider lists fixed versions of Vijeo Designer, Machine Expert, and firmware bundles for Modicon/PacDrive lines — for example, Vijeo Designer v6.3.1 (and hotfix/service pack variants) and Machine Expert v2.2 are the vendor‑called updates that deliver runtime fixes and, in some cases, remove vulnerable components (e.g., SoftSPS removal in Machine Expert v2.2). For specific controller firmware the vendor distributes patched firmware via the Schneider Electric Software Update (SESU) system or Customer Care channels.
• End‑of‑life / migration guidance: For SKUs that have reached end‑of‑commercialization (Magelis XBT, or legacy Modicon LMC078/M218), Schneider recommends migration to newer product lines because no fixes are planned. Customers running EOL hardware should prioritize network isolation and migration planning.
• Workarounds where fixes are not available: Schneider provide — enable user management and enforced strong passwords, activate encrypted communications and project encryption, enable CODESYS “Implicit Checks” and logic hardening, avoid POINTER/MEMMOVE usage in logic, and restrict programming ports at firewalls. These mitigations are repeated throughout the advisory as immediate actions customers must take until firmware updates can be applied.

Independent coverage (Microsoft, security vendors and industry reporters) corroborates the critical nature of the flaws and recommends urgent patching to CODESYS v3.5.19.0 or later at the runtime level, and for device vendors to release firmware updates that incorporate that fixed SDK level.

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Practical remediation checklist (prioritized, operational)​

• Inventory and identify
• Inventory every device that may embed CODESYS (PLCs, HMIs, developer workstations, machine controllers, soft‑runtimes). Use vendor scan tools, Microsoft’s forensics/detection tool or network asset discovery to find hosts with CODESYS‑protocol ports exposed.
• Segregate and isolate
• Immediately place vulnerable controllers behind strict firewall rules. Block programming/management ports (commonly UDP 1740–1743, TCP 11740–11743, and the vendor‑listed ports such as TCP 1105 / TCP 484 for some HMI runtimes) where feasible. Ensure there is no direct access from enterprise internet‑facing networks.
• Apply vendor fixes
• On engineering workstations, update to the vendor‑released versions (for example Vijeo Designer v6.3.1 and Machine Expert v2.2 as called out in vendor notices) and follow Schneider’s firmware update steps for each controller family. Apply fixes in a staging environment, then schedule controlled maintenance windows for production updates.
• Harden runtime and projects
• Enable user management with forced strong passwords, activate project encryption / enhanced security settings, and enable any recommended runtime integrity checks (Implicit Checks, project encryption). Avoid unsafe function blocks in PLC code: do not use POINTER where avoidable; minimize MEMMOVE and similar unsafe operations on untrusted inputs.
• Restrict access
• Lock down VPN and remote access (use MFA, limit accounts), restrict physical access to controllers and engineering laptops, and remove or limit service accounts. Ensure the minimum privilege model for any user permitted to upload or modify PLC projects.
• Monitor and detect
• Use network IDS/IPS signatures tuned to detect anomalous CODESYS protocol behaviour; monitor for rapid or anomalous project downloads, repeated malformed requests, and unexpected service restarts. Microsoft and other researchers published detection guidance and heuristics — integrate those into your SOC playbooks.
• Plan for EOL hardware
• If devices are EOL and Schneider has no patch planned, create a migration plan. Short of replacement, apply aggressive network isolation and compensating controls (air‑gapping where possible, physical access controls, strict firewall ACLs).

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Detection and threat‑hunting guidance​

• Scan for exposed CODESYS ports (network scans on TCP 11740/TCP 11741 and UDP 1740 and neighbours). Exposed ports are a strong indicator of internet or WAN‑accessible control channels that should not be reachable from untrusted networks.
• Hunt logs for repeated malformed tag‑decode sequences, unexpected filetransfer requests, or authentication failures followed by suspicious payloads that match the CODESYS packet structure. Microsoft and some security vendors published packet‑level indicators and forensics tools to assist with this triage.
• Check engineering workstations and developer tool versions: patched Vijeo Designer / Machine Expert versions indicate remediation progress for many deployed controllers. If an engineering workstation is behind, it may continue to upload vulnerable runtime images to controllers.

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Risk assessment — strengths and remaining concerns​

Strengths and positive indicators

• Schneider Electric has published a comprehensive product matrix, remediation guidance and explicit firmware/software versions for many affected SKUs — customers now have direct upgrade paths in many cases. The vendor also removed or deprecated vulnerable components where possible (for example SoftSPS removal in Machine Expert v2.2) rather than relying solely on patches.
• Microsoft’s public technical write‑up and tool release gave operators concrete detection and identification resources, accelerating enterprise and vendor response. That public research also pushed device vendors to integrate the CODESYS SDK patches into device firmware quickly.

Risks and caveats

• Authentication is required for many of these flaws, but authentication is not a guaranteed barrier in the real world. Weak/default credentials, exposed engineering stations, and chained vulnerabilities (or credential theft) can turn an “authenticated” exploit into a remotely trivial attack.
• Some product lines and field devices are EOL with no planned fixes. Those devices remain high‑risk assets until replaced or fully isolated; the operational complexity and capital costs of replacing PLCs/HMIs in factory floors mean many customers will run EOL firmware for prolonged periods, creating long tails of risk.
• Patching controllers often requires planned downtime, and firmware upgrades can introduce functional or timing changes in deterministic control loops; many operations teams delay updates until test cycles complete, leaving a window of exposure. Patching logistics, regression testing and rollback planning remain non‑trivial for OT teams.
• Public reporting and exploit code proliferation: while there were no widespread public exploit campaigns at the time of the original disclosures, the detailed technical write‑ups and proof‑of‑concepts published by researchers increase the chance of weaponization by opportunistic attackers. Continued vigilance is required.

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Where verification is uncertain — cautionary flags​

• Exact per‑SKU firmware thresholds: Schneider’s advisory gives version guidance for many families, but the mapping between a particular controller part number, a vendor‑specific firmware bundle and the embedded CODESYS SDK version is sometimes nontrivial. Operators should not assume a device is fixed based on a single figure cited in secondary sources; vall, firmware build number and engineering tool version against Schneider’s published remediation matrix or Customer Care.
• Exploitability nuance: public advisories emphasize that exploitation often requires some level of authentication and protocol knowledge. While many CVEs are highly severe on paper, the practical complexity of constructing an exploit that reliably yields RCE differs by device and network posture. Treat “requires authentication” as a reduced but not absent risk — attackers routinely chain weaknesses.

If any claim about a specific firmware number or a per‑device “fixed in version X.Y” is critical to your remediation timeline, validate directly with Schneider Electric support and the device’s update package notes — vendor‑published change logs and SESU distribution metadata are authoritative for final upgrade decisions.

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Recommendations for IT and OT operators (concise)​

• Treat these CODESYS runtime vulnerabilities as operationally critical and prioritize devices that are internet‑exposed, WAN‑reachable, or connected to shared enterprise networks.
• If you cannot patch immediately, enforce strict network segmentation, block programming ports, enable project encryption and strong user management, and use whitelisting on engineering workstations.
• Prioritize patching of engineering tools (Vijeo Designer / Machine Expert) as well as controller firmware to avoid reintroducing vulnerable runtime images.
• For EOL devices, implement compensating controls (air‑gap or one‑way data diodes where possible) and begin procurement for replacement hardware.
• Subscribe to vendor security notifications and coordinate scheduled maintenance windows with operational owners — remediation in OT requires careful change control.

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Conclusion​

The CODESYS V3 runtime vulnerabilities represent a systemic class of memory‑safety and protocol‑parsing flaws that affect many vendors — Schneider Electric among them — and translate into real operational risk for industrial environments. Schneider’s published patches and guidance give operators concrete remediation paths for many product families, but gaps remain: legacy devices without planned fixes, the operational burden of firmware upgrades, and the pragmatic reality that authentication requirements can be bypassed in poorly managed networks.
For safety and continuity, immediate actions are straightforward: inventory, isolate, patch engineering tools and controllers where fixes exist, harden project and runtime configurations, and treat EOL devices as high‑risk assets requiring rapid mitigation or replacement. Combine those steps with active detection (network scanning, IDS signatures and the vendor/researcher detection guidance) and a structured OT patch governance process to reduce the window of exposure. If precise firmware or hotfix versions are required for scheduling maintenance, confirm the exact build numbers for each device with Schneider Electric Customer Care and use the Schneider SESU distribution and advisory documentation as your authoritative reference.

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Source: CISA Schneider Electric devices using CODESYS Runtime | CISA