Gradio's dropdown component pre-process step does not limit the values to those in the dropdown list

Summary

### Impact **What kind of vulnerability is it? Who is impacted?**

This vulnerability is a **data validation issue** in the Gradio `Dropdown` component's pre-processing step. Even if the `allow_custom_value` parameter is set to `False`, attackers can bypass this restriction by sending custom requests with arbitrary values, effectively breaking the developer’s intended input constraints. While this alone is not a severe vulnerability, it can lead to more critical security issues, particularly when paired with other vulnerabilities like file downloads from the user's machine.

### Patches Yes, this issue is addressed in `gradio>=5.0`. Please upgrade to the latest version to resolve the problem.

### Workarounds **Is there a way for users to fix or remediate the vulnerability without upgrading?**

To mitigate the issue without upgrading, developers can add manual validation in their prediction function to check the received values against the allowed dropdown values before processing them.