CVE-2018-7790 in Modicon M221
Summary
by MITRE
An Information Management Error vulnerability exists in Schneider Electric's Modicon M221 product (all references, all versions prior to firmware V1.6.2.0). The vulnerability allows unauthorized users to replay authentication sequences. If an attacker exploits this vulnerability and connects to a Modicon M221, the attacker can upload the original program from the PLC.
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Analysis
by VulDB Data Team • 05/29/2026
The CVE-2018-7790 vulnerability represents a critical information management error within Schneider Electric's Modicon M221 programmable logic controller that affects all versions prior to firmware revision V1.6.2.0. This flaw resides in the authentication mechanism implementation and fundamentally undermines the security posture of industrial control systems by enabling unauthorized access to critical operational assets. The vulnerability operates at the protocol level where authentication sequences can be replayed by malicious actors, effectively bypassing the intended security controls that should protect industrial automation equipment from unauthorized modifications. This type of vulnerability falls under the CWE-305 authentication weakness category, specifically addressing the improper handling of authentication tokens and sequence numbers that should prevent replay attacks in industrial communication protocols.
The technical exploitation of this vulnerability occurs through the manipulation of authentication sequences that are typically designed to be one-time use or time-bound to prevent unauthorized access. When an attacker successfully replays these sequences, they can establish unauthorized connections to the Modicon M221 device, gaining access to the system's operational capabilities. The most significant consequence of this vulnerability is the ability for attackers to upload original programs directly to the PLC, which represents a complete compromise of the industrial control system's integrity and operational safety. This capability allows adversaries to modify the control logic, potentially causing production disruptions, safety hazards, or even physical damage to industrial processes. The vulnerability demonstrates a fundamental flaw in the cryptographic implementation and session management protocols used by the device.
From an operational impact perspective, this vulnerability creates a severe risk to industrial environments that rely on Modicon M221 controllers for critical automation functions. The ability to upload original programs means attackers can modify control logic in real-time, potentially causing equipment malfunctions, safety system failures, or production line shutdowns. The vulnerability's exploitation requires minimal technical expertise compared to other industrial control system attacks, making it particularly dangerous for operational technology environments where security awareness may be limited. Organizations using affected Modicon M221 devices face significant risk of supply chain compromise, as the vulnerability could be exploited to gain persistent access to industrial networks. This type of attack aligns with tactics described in the ATT&CK framework under the "Initial Access" and "Execution" phases, specifically targeting industrial control systems through authentication bypass techniques.
The mitigation strategy for CVE-2018-7790 primarily involves updating the Modicon M221 firmware to version V1.6.2.0 or later, which addresses the authentication replay vulnerability through improved cryptographic implementation and session management. Organizations should also implement network segmentation to isolate industrial control systems from general enterprise networks, reducing the attack surface available to potential adversaries. Additional security measures include implementing robust network monitoring to detect anomalous authentication patterns and unauthorized program uploads, as well as establishing strict access control policies that limit who can connect to industrial control equipment. Security teams should also consider implementing intrusion detection systems specifically designed for industrial control protocols to identify replay attacks and other suspicious activities. The vulnerability highlights the importance of maintaining current firmware versions in industrial environments and demonstrates how seemingly minor authentication flaws can result in complete system compromise, emphasizing the need for comprehensive industrial cybersecurity practices that address both network and application-level security controls.