CVE-2018-8836 in 750 PLC
Summary
by MITRE
Wago 750 Series PLCs with firmware version 10 and prior include a remote attack may take advantage of an improper implementation of the 3 way handshake during a TCP connection affecting the communications with commission and service tools. Specially crafted packets may also be sent to Port 2455/TCP/IP, used in Codesys management software, which may result in a denial-of-service condition of communications with commissioning and service tools.
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Analysis
by VulDB Data Team • 02/08/2021
The CVE-2018-8836 vulnerability affects Wago 750 Series Programmable Logic Controllers operating with firmware version 10 or earlier, presenting a significant security risk to industrial control systems. This vulnerability stems from an improper implementation of the TCP three-way handshake mechanism during TCP connection establishment, which fundamentally compromises the integrity of network communications between the PLC and its commissioning and service tools. The flaw specifically impacts the TCP communication channel used for maintaining secure connections to the device, creating an attack surface that adversaries can exploit to disrupt critical industrial operations. The vulnerability is particularly concerning because it affects the core communication protocols that industrial systems rely upon for configuration, monitoring, and maintenance activities.
The technical implementation flaw manifests in the way the PLC handles TCP connection establishment processes, where the device fails to properly validate or process incoming TCP packets during the three-way handshake sequence. This improper handling creates opportunities for attackers to send specially crafted packets to port 2455/tcp, which is the designated port for Codesys management software communication. The Codesys protocol is widely used in industrial automation environments for programming and configuring PLC devices, making this vulnerability particularly dangerous as it directly targets the management interface that operators use for essential system maintenance and configuration tasks. The vulnerability's impact is amplified by the fact that it operates at the network protocol level, making it possible to exploit from remote locations without requiring physical access to the device.
The operational impact of this vulnerability extends beyond simple denial-of-service conditions, as it fundamentally undermines the reliability and availability of industrial control systems. When exploited, the vulnerability can cause complete disruption of communications between the PLC and its management tools, preventing operators from performing critical configuration changes, software updates, or diagnostic procedures. This disruption can lead to extended downtime for industrial processes, potentially resulting in production losses, safety risks, and increased operational costs. The vulnerability's remote exploitability means that attackers can target these devices from anywhere on the network, making it particularly dangerous in environments where industrial systems are connected to corporate networks or the internet. Organizations relying on Wago 750 Series PLCs face significant operational risks as this vulnerability can be exploited by both malicious actors and automated scanning tools looking for vulnerable industrial targets.
Mitigation strategies for CVE-2018-8836 should focus on both immediate protective measures and long-term architectural improvements to industrial network security. Organizations should prioritize updating affected PLC firmware to versions that properly implement TCP connection handling, which aligns with the principle of defense in depth as outlined in the NIST Cybersecurity Framework. Network segmentation should be implemented to isolate industrial control systems from general corporate networks, reducing the attack surface and limiting potential exploitation paths. The vulnerability's characteristics align with CWE-119, which deals with improper access to resources via weak input validation, and the attack pattern maps to ATT&CK technique T1071.004 for application layer protocol usage. Access control measures should be enforced at network boundaries using firewalls to restrict access to port 2455/tcp to only authorized management systems, while also implementing network monitoring to detect anomalous TCP connection patterns that might indicate exploitation attempts. Regular vulnerability assessments and penetration testing should be conducted to identify similar protocol implementation flaws across industrial control system environments.