Arduino Create Agent vulnerable to Reflected Cross-Site Scripting

Summary

The Arduino Create Agent allows users to use the Arduino Create applications to upload code to any USB connected Arduino board directly from the browser. A vulnerability in versions prior to 1.3.6 affects the endpoint `/certificate.crt` and the way the web interface of the ArduinoCreateAgent handles custom error messages. An attacker that is able to persuade a victim into clicking on a malicious link can perform a Reflected Cross-Site Scripting attack on the web interface of the create agent, which would allow the attacker to execute arbitrary browser client side code. Version 1.3.6 contains a fix for the issue.