baserCMS: stored widget data deserialized, enabling command execution on page load

baserCMS is a website development framework. In versions 5.0.0 before 5.3.2 and 5.4.0 before 5.4.2, the widget-area entity serializes widgets only when the submitted value is an array, allowing a string submitted through the admin JSON API to be stored unchanged. Entity reads, including front-end rendering and API responses, deserialize the stored value with unserialize() without an allowed_classes restriction, accepting both raw and base64-encoded serialized data. An administrator, or an attacker who obtains widget-write capability through a separate vulnerability such as chained XSS, can plant an object graph that subsequently triggers on unauthenticated page requests. Two demonstrated gadget chains in the default dependency set use composer/composer ProcessExecutor::startJob() with Process::fromShellCommandline(), or logiscape/mcp-sdk-php StdioTransport::connect() with StdioServerParameters, to reach proc_open() and execute commands as the web-server user. Deserialization bypasses constructor-based readonly safeguards, and the stored payload can execute repeatedly until the database row is repaired. Unauthenticated page access is a trigger after privileged payload storage, not an unauthenticated means of initially planting the payload. This issue has been patched in versions 5.3.2 and 5.4.2.