Bypassing the Sound Blaster's new firmware signature check

I recently demonstrated a few vulnerabilities in the Sound Blaster Katana V2/V2X/SE which allowed me to hijack the device over Bluetooth and turn it into an attacker-controlled keyboard peripheral, injecting keystrokes into the connected machine. Creative recently published a new firmware (version 1.20.260617.1110) to address these issues. In this article, I take a deep dive into the changes and highlight why they're not sufficient to stop the same attack that I described.