CVE-2018-7758 in MiCOM Px4x
Summary
by MITRE
A denial of service vulnerability exists in Schneider Electric's MiCOM Px4x (P540 range excluded) with legacy Ethernet board, MiCOM P540D Range with Legacy Ethernet Board, and MiCOM Px4x Rejuvenated could lose network communication in case of TCP/IP open requests on port 20000 (DNP3oE) if an older TCI/IP session is still open with identical IP address and port number.
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Analysis
by VulDB Data Team • 01/27/2020
The vulnerability described in CVE-2018-7758 represents a critical denial of service weakness affecting Schneider Electric's MiCOM Px4x series protective relays, excluding the P540 range, as well as the MiCOM P540D Range with legacy Ethernet boards and rejuvenated Px4x devices. This issue specifically manifests when the affected equipment experiences TCP/IP open requests on port 20000, which is designated for DNP3 over Ethernet communications. The flaw becomes particularly problematic when an older TCI/IP session remains active with the same IP address and port combination, creating a scenario where network connectivity is disrupted. The vulnerability stems from inadequate session management and connection handling mechanisms within the legacy Ethernet board implementations of these industrial control devices, which are commonly deployed in critical infrastructure environments including power distribution systems, water treatment facilities, and other industrial automation applications.
The technical implementation of this vulnerability involves a race condition or improper state handling within the network stack of the affected devices. When a new TCP/IP connection attempt occurs on the DNP3oE port 20000 while an existing session with identical source IP and port is still active, the device fails to properly process or reject the conflicting connection request. This results in the device losing its network communication capabilities, effectively rendering the protective relay non-functional from a network perspective. The root cause can be categorized under CWE-400, which addresses "Uncontrolled Resource Consumption" or "Resource Exhaustion," specifically manifesting as a denial of service condition where network resources become unavailable due to improper connection handling. The vulnerability operates at the network protocol level and represents a failure in proper TCP connection state management, where the device cannot distinguish between legitimate new connections and conflicting legacy sessions.
From an operational impact perspective, this vulnerability poses significant risks to industrial control systems and critical infrastructure environments where these devices are deployed. The loss of network communication can result in complete loss of remote monitoring and control capabilities for protective relays, potentially leading to extended downtime for critical power distribution systems. Network administrators and operators may find their ability to manage and monitor these devices completely compromised, as the affected systems become unreachable via their standard network interfaces. The vulnerability's exploitation requires minimal effort and can be accomplished through simple network scanning or connection attempts, making it particularly dangerous in environments where physical access is limited or restricted. According to ATT&CK framework, this vulnerability maps to T1499.004, which covers "Endpoint Denial of Service" and potentially T1566.001 for "Phishing" if exploitation occurs through network-based attacks. The impact extends beyond simple service disruption as these devices are fundamental to power system protection and control, potentially leading to cascading failures in grid operations.
Mitigation strategies for CVE-2018-7758 should prioritize immediate firmware updates from Schneider Electric, as the vendor has released patches addressing this specific issue. Network segmentation and access control measures should be implemented to restrict access to port 20000, particularly in environments where unauthorized access is possible. Implementing network monitoring solutions that can detect unusual connection patterns or session conflicts on the affected port can provide early warning of potential exploitation attempts. Device administrators should also consider disabling unused network services and implementing strict firewall rules that only allow connections from known trusted IP addresses. The vulnerability highlights the importance of maintaining up-to-date firmware in industrial control systems, as legacy devices often contain unpatched vulnerabilities that can be exploited by attackers. Organizations should conduct comprehensive vulnerability assessments of their industrial control system networks to identify all potentially affected devices and implement layered security controls to minimize the risk of exploitation. Additionally, regular network audits and connection monitoring should be established to detect anomalous behavior that might indicate exploitation attempts.