^{CVE-2020-7537:}Improper Check for Unusual Conditions in Schneider Electric Modicon Controllers

Overview

This vulnerability (CVE-2020-7537) affects multiple Schneider Electric Modicon industrial controllers, which are widely used in industrial control systems and critical infrastructure. The issue stems from improper validation of Read Physical Memory requests sent over the Modbus protocol. When these controllers receive specially crafted malformed requests, they fail to properly handle exceptional conditions, which can trigger a denial of service condition. This could potentially disrupt industrial processes, manufacturing operations, or other critical systems that rely on these controllers. The vulnerability is particularly concerning in industrial environments where system availability is crucial for safety and operational continuity.

Remediation

1. Update firmware to the latest version as recommended by Schneider Electric in their security advisory (SEVD-2020-343-08).
2. If immediate patching is not possible, implement network segmentation to isolate the affected controllers from untrusted networks.
3. Use firewalls or access control lists to restrict Modbus communications to trusted sources only.
4. Monitor network traffic for suspicious Modbus requests, particularly those targeting memory read operations.
5. Implement a defense-in-depth strategy including physical security controls and network monitoring.
6. Contact Schneider Electric technical support for product-specific guidance if needed.
7. Follow ICS-CERT recommendations for securing industrial control systems.

References

1. Schneider Electric Security Advisory: https://www.se.com/ww/en/download/document/SEVD-2020-343-08/
2. CWE-754: Improper Check for Unusual or Exceptional Conditions: https://cwe.mitre.org/data/definitions/754.html
3. ICS-CERT Recommended Practices: https://www.cisa.gov/ics/recommended-practices
4. Modbus Organization: https://modbus.org/tech.php
5. NIST Guide to Industrial Control Systems Security: https://csrc.nist.gov/publications/detail/sp/800-82/rev-2/final