PLCnext Engineer before 2026.6: unsigned plugin archive entries overwrite signed assemblies and run code

The PFI plugin framework deploys executable assemblies (DLLs) from a signed plugin package into the local plugin repository and loads them via reflection, but the deployment routine processes archive entries that were never covered by the signature verification. An unauthenticated local attacker can replace an unsigned DLL outside the signed prefix in the archive passes verification and overwrites the legitimate signed assembly at the same destination path. The plugin loader then instantiates the attacker-supplied code without any additional integrity check resulting in a full compromise of the affected systems.