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.
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. cisco rv042 firmware
PSA: Cisco RV042 Firmware – Final Version & Security Warnings (2024/2025) Final firmware = 4
I know many of us are still running the trusty old RV042 dual-WAN router in home labs or for legacy VPN links, despite Cisco officially ending support for the Small Business RV0xx series years ago. cisco rv042 firmware