CVE-2018-7856 Schneider Electric CVE debrief

Who should care

OT operators, plant engineers, system integrators, and asset owners running Schneider Electric Modicon M580, M340, Quantum, or Premium controllers, especially where Modbus/TCP is reachable from broader networks or remote access paths.

Technical summary

The issue is described as an uncaught exception that can occur when writing invalid memory blocks to the controller over Modbus, leading to possible denial of service. The advisory ties the problem to multiple Schneider Electric controller and firmware lines, with remediation varying by platform: fixed firmware is available for some products, while legacy Quantum and Premium controllers are also described as end-of-life and may require migration plus compensating controls.

Defensive priority

High

Recommended defensive actions

• Update affected firmware to vendor-fixed versions where available: M580 to SV4.20 or above, M340 to v3.60 or above, and Quantum to v3.60 where supported.
• After upgrading M580 or M340, update the engineering workstation software, rebuild projects, and transfer the revised projects to the controller as directed by Schneider Electric.
• For Premium and Quantum systems, apply the vendor-specified fixes or migrate to supported platforms when feasible, since the advisory notes these product lines are end of life.
• Restrict Modbus/TCP exposure on port 502 with network segmentation, firewalls, and access control lists so only authorized hosts can reach controllers.
• Enable application passwords and follow Schneider Electric secure-communications guidance, including IPsec-based options where supported.
• Validate controller configuration against the vendor manuals cited in the advisory, including ACL and secure-communications chapters, before returning systems to service.

Evidence notes

The debrief is based on the CISA-hosted CSAF advisory for CVE-2018-7856 and Schneider Electric security notices referenced there. The source item states the issue as an uncaught exception during invalid Modbus memory-block writes, and lists vendor fixes plus compensating controls. Timing context comes from the supplied CVE publication date of 2019-05-14 and the source item modification date of 2026-04-23; no later generation or review date is treated as the CVE issue date. The corpus contains both a CVSS v4.0 statement in the description and a CVSS v3.1 vector in the CSAF metadata, so the narrative avoids overcommitting to a single scoring framework beyond the provided severity context.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.