Hyland OnBase versions prior to 17.0.2.87 (other versions may be affected) are vulnerable to unauthenticated remote code execution via insecure deserialization on the .NET Remoting TCP channel. The service registers a listener on port 6031 with the URI endpoint TimerServer, implemented in Hyland.Core.Timers.dll. This endpoint deserializes untrusted input using the .NET BinaryFormatter, allowing attackers to execute arbitrary code under the context of NT AUTHORITYSYSTEM.
The product deserializes untrusted data without sufficiently verifying that the resulting data will be valid.
It is often convenient to serialize objects for communication or to save them for later use. However, deserialized data or code can often be modified without using the provided accessor functions if it does not use cryptography to protect itself. Furthermore, any cryptography would still be client-side security – which is a dangerous security assumption. Data that is untrusted can not be trusted to be well-formed. When developers place no restrictions on “gadget chains,” or series of instances and method invocations that can self-execute during the deserialization process (i.e., before the object is returned to the caller), it is sometimes possible for attackers to leverage them to perform unauthorized actions, like generating a shell.