CVE-2020-7502 in Modicon M218 Logic Controller
Summary
by MITRE
A CWE-787: Out-of-bounds Write vulnerability exists in Modicon M218 Logic Controller (Firmware version 4.3 and prior), which may cause a Denial of Service when specific TCP/IP crafted packets are sent to the Modicon M218 Logic Controller.
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Analysis
by VulDB Data Team • 06/17/2020
The vulnerability identified as CVE-2020-7502 represents a critical out-of-bounds write condition classified under CWE-787, affecting Modicon M218 Logic Controllers running firmware versions 4.3 and earlier. This flaw exists within the TCP/IP stack implementation of the industrial control device, creating a significant security risk for operational technology environments. The vulnerability manifests when the controller receives specifically crafted TCP/IP packets that trigger memory corruption during packet processing. The Modicon M218, manufactured by Schneider Electric, is a compact programmable logic controller widely deployed in industrial automation systems, making this vulnerability particularly concerning for critical infrastructure sectors.
The technical implementation of this vulnerability stems from inadequate input validation within the controller's network communication protocol handling. When the M218 Logic Controller processes malformed TCP packets, the system fails to properly bounds-check memory allocations before writing data to memory buffers. This allows an attacker to craft packets that exceed the allocated buffer size, resulting in memory corruption that can trigger system instability. The out-of-bounds write condition occurs during the parsing of TCP/IP headers or payload data, where the controller's firmware does not validate the length parameters of incoming network data against predefined buffer limits. This type of vulnerability falls under the ATT&CK technique T1210 - Exploitation of Remote Services, as it leverages network-based attack vectors to compromise system integrity.
The operational impact of this vulnerability extends beyond simple denial of service, potentially compromising the reliability of industrial control systems that depend on continuous operation. When triggered, the out-of-bounds write can cause the Modicon M218 to crash, reboot unexpectedly, or enter an unstable state that prevents normal industrial processes from functioning correctly. In critical manufacturing environments, this disruption can lead to production halts, quality control failures, and potential safety hazards. The vulnerability's exploitation requires network access to the controller, making it accessible to attackers who can reach the device through unsecured network segments or compromised adjacent systems. The lack of authentication requirements for the affected TCP/IP endpoints further amplifies the risk, as the vulnerability can be exploited without prior authorization or credentials.
Mitigation strategies for CVE-2020-7502 should focus on both immediate protective measures and long-term firmware updates. The most effective immediate solution involves applying the firmware update released by Schneider Electric that addresses the specific bounds-checking issue in the TCP/IP processing module. Network segmentation and access control measures should be implemented to limit direct network access to industrial controllers, reducing the attack surface for remote exploitation attempts. Firewalls and network access control lists should be configured to restrict TCP port access to only trusted administrative systems. The vulnerability demonstrates the importance of secure coding practices and input validation in industrial control systems, aligning with CWE guidelines that emphasize proper bounds checking and memory management. Organizations should also implement network monitoring to detect unusual traffic patterns that might indicate exploitation attempts, as well as establish incident response procedures for handling potential controller instability. Regular security assessments of industrial control systems should include evaluation of firmware versions and patch management processes to ensure timely remediation of known vulnerabilities.