CVE-2020-24686 in AC500 V2
Summary
by MITRE • 02/26/2021
The vulnerabilities can be exploited to cause the web visualization component of the PLC to stop and not respond, leading to genuine users losing remote visibility of the PLC state. If a user attempts to login to the PLC while this vulnerability is exploited, the PLC will show an error state and refuse connections to Automation Builder. The execution of the PLC application is not affected by this vulnerability. This issue affects ABB AC500 V2 products with onboard Ethernet.
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Analysis
by VulDB Data Team • 03/05/2021
The vulnerability identified as CVE-2020-24686 represents a significant denial-of-service condition within ABB AC500 V2 products that utilize onboard Ethernet connectivity. This flaw specifically targets the web visualization component of the programmable logic controller, creating a scenario where legitimate users lose critical remote access to monitor and control industrial processes. The affected systems operate within industrial control environments where continuous visibility and operational control are paramount for maintaining production integrity and safety protocols.
Technical exploitation of this vulnerability manifests through mechanisms that cause the web visualization interface to become unresponsive or completely cease operation. The flaw operates at the application layer of the network stack, specifically targeting the web server component that handles user interface requests for PLC status monitoring. When successfully exploited, the vulnerability creates a state where the PLC's web interface becomes non-functional, effectively cutting off remote operators from accessing real-time process data and system status information. This represents a direct violation of the availability principle in the CIA triad, as it prevents authorized users from accessing critical operational data.
The operational impact extends beyond simple service disruption, as the vulnerability specifically interferes with authentication mechanisms and connection protocols used by the Automation Builder software. When users attempt to establish connections to the PLC during exploitation, the system displays error states and actively refuses new connection attempts, effectively creating a complete communication barrier between operators and the industrial control system. This behavior demonstrates characteristics consistent with CWE-400, which addresses unchecked resource consumption and system resource exhaustion vulnerabilities that can lead to denial-of-service conditions. The vulnerability does not compromise the core PLC execution engine, indicating it operates at a level above the runtime application but below the physical hardware, creating a specific attack surface that targets the communication and presentation layers.
From a cybersecurity perspective, this vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks targeting industrial control systems. The attack vector likely involves sending malformed requests or exploiting buffer overflow conditions within the web visualization component that causes the application to crash or enter an unrecoverable state. The fact that the PLC application execution remains unaffected suggests this vulnerability operates through a separate process or service that handles user interface presentation rather than core control functions, though this distinction is critical for operational security planning and incident response protocols.
Mitigation strategies should focus on network segmentation and access control implementation to limit exposure of affected systems to untrusted networks. Organizations should implement robust network monitoring to detect unusual traffic patterns that might indicate exploitation attempts, while also maintaining regular firmware update schedules to ensure the latest security patches are deployed. The vulnerability's specific targeting of web visualization components suggests that disabling or restricting web access to these systems when not required could serve as an effective temporary workaround. Additionally, implementing intrusion detection systems with signatures specific to known exploit patterns for industrial control system vulnerabilities would enhance overall defensive posture against similar threats.