Final firmware = 4.2.3.08. Don't expose to WAN. Use an old Firefox fork to manage it. Retire it if you care about security.

PSA: Cisco RV042 Firmware – Final Version & Security Warnings (2024/2025)

Stay safe out there.

I recently had to rebuild one and ran into the usual headache of finding the correct firmware without a support contract. Here is the current state of play for anyone else hunting for it.