Kanboard is project management software that focuses on the Kanban methodology. Prior to version 1.2.47, an unsafe deserialization vulnerability in the ProjectEventActvityFormatter allows admin users the ability to instantiate arbitrary php objects by modifying the event[data] field in the project_activities table. A malicious actor can update this field to use a php gadget to write a web shell into the /plugins folder, which then gives remote code execution on the host system. This issue has been patched in version 1.2.47.
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.