Some TwinCAT OPC UA Server and IPC Diagnostics UA Server versions from Beckhoff Automation GmbH & Co. KG are vulnerable to denial of service attacks. The attacker needs to send several specifically crafted requests to the running OPC UA server. After some of these requests the OPC UA server is no longer responsive to any client. This is without effect to the real-time functionality of IPCs.
UPDATE A - 11.05.2021
Please note that some hardware products from Beckhoff are shipped with a TwinCAT OPC UA Server pre-installed. In some cases the server is enabled by default.
IPC Diagnostics UA Server (contained in Beckhoff’s Windows images)
The version numbers named above always refer to the version number which is accessible via OPC UA at the server via the standard OPC UA node /Objects/Server/ServerStatus/BuildInfo/SoftwareVersion and on Windows also as the file property "File version" of the file TcOpcUaServer.exe for TwinCAT OPC UA Server respectively the file DevMgrSvr-UA.exe for IPC Diagnostics UA Server.
UPDATE A - 11.05.2021
Please note that IPC products from Beckhoff are shipped with an IPC Diagnostics UA Server pre-installed. While on Windows CE it is disabled by default all other Windows images have it enabled by default.
The default installation path and its permissions for the TwinCAT runtime allow a local user to replace or modify executables other users of the same system might execute. The issue does not apply for installations underneath C:\Program Files.
Beckhoff’s TwinCAT RT network driver for Intel 8254x and 8255x is providing EtherCAT functionality. The driver implements real-time features. Except for Ethernet frames sent from real-time functionality, all other Ethernet frames sent through the driver are not padded if their payload is less than the minimum Ethernet frame size. Instead, arbitrary memory content is transmitted within in the padding bytes of the frame. Most likely this memory contains slices from previously transmitted or received frames.
In case TwinCAT is configured to use the Profinet driver, a denial of service of the controller could be reached by sending special packets to the device.