Advisory2026-12_VDE-2026-097

CODESYS Control Runtime - Improper Synchronization in Monitoring

The monitoring functionality of affected CODESYS Control runtime systems processes read and write requests to PLC application data sent by the CODESYS Development System and other clients such as HMIs. Due to improper synchronization in the CmpMonitor2 component when processing concurrent requests from multiple clients, incorrect data may be read or written, potentially resulting in unexpected behavior of the affected product. PLCs based on the CODESYS Runtime Toolkit or CODESYS Safety SIL2 are affected if they allow simultaneous access by two or more clients via the CODESYS protocol. In CODESYS Development System 3, simultaneous access to the included Simulation Runtime can only occur when access by an external client, such as an HMI, has been explicitly enabled through dedicated configuration. The default configuration of CODESYS Development System 3 is not affected. The vulnerability can be exploited by an authenticated remote attacker with monitoring access by issuing concurrent requests to an affected product.