CVE-2020-20741 in CX9020
Summary
by MITRE • 07/24/2021
Incorrect Access Control in Beckhoff Automation GmbH & Co. KG CX9020 with firmware version CX9020_CB3011_WEC7_HPS_v602_TC31_B4016.6 allows remote attackers to bypass authentication via the "CE Remote Display Tool" as it does not close the incoming connection on the Windows CE side if the credentials are incorrect.
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Analysis
by VulDB Data Team • 07/28/2021
The vulnerability identified as CVE-2020-20741 represents a critical access control flaw within the Beckhoff CX9020 industrial automation device running specific firmware versions. This issue affects the Windows CE-based embedded system that serves as the foundation for Beckhoff's automation solutions. The device operates in industrial environments where secure access controls are paramount for operational continuity and safety. The vulnerability specifically targets the "CE Remote Display Tool" component which handles remote authentication requests for system access. Security researchers have identified that this particular implementation fails to properly manage connection states when authentication credentials are invalid, creating a persistent security weakness that remote attackers can exploit.
The technical root cause of this vulnerability stems from improper connection state management within the Windows CE operating system environment. When an unauthorized user attempts to establish a remote connection through the CE Remote Display Tool, the system accepts the initial connection request but fails to terminate the session properly upon credential validation failure. This behavior creates a persistent connection state that can be leveraged by attackers to bypass authentication mechanisms entirely. The flaw exists at the protocol level where the system does not enforce proper connection closure procedures, allowing attackers to maintain access to the device's resources even after failed authentication attempts. This represents a classic case of inadequate input validation and connection handling as outlined in CWE-284, which addresses improper access control mechanisms.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass potential industrial control system compromise. Attackers can exploit this weakness to gain persistent access to the CX9020 device, potentially leading to system disruption, data manipulation, or even physical safety risks in industrial environments. The vulnerability particularly affects environments where the device operates as a critical component in automation systems, where unauthorized access could lead to production downtime or safety incidents. The remote nature of the attack means that threat actors do not require physical access to the device, making this vulnerability particularly dangerous in networked industrial settings. This aligns with ATT&CK technique T1110.003 which covers credential guessing and brute force attacks that exploit weak authentication controls.
Mitigation strategies for this vulnerability require immediate firmware updates from Beckhoff to address the specific connection handling flaw in the CE Remote Display Tool. Organizations should implement network segmentation to isolate industrial control systems from general network access, reducing the attack surface for remote exploitation attempts. Additional protective measures include configuring firewalls to restrict access to the specific ports used by the remote display tool, implementing multi-factor authentication where possible, and establishing continuous monitoring for unauthorized connection attempts. Security teams should also conduct comprehensive vulnerability assessments of all industrial control systems to identify similar connection handling flaws that may exist in other embedded devices. The remediation process must include thorough testing of firmware updates in controlled environments before deployment to ensure operational stability while addressing the security weakness. Organizations should also implement network access controls and regular security audits to prevent similar vulnerabilities from emerging in their industrial control infrastructure.