Busybox is a multi-function binary which allows embedded devices that don't have as much space and RAM as a real Linux computer to have access to a wide range of shell tools used by the OS, normally provided as separate packages. Things like the shell interpreter (ash), awk, grep, ping, the DHCP client, etc... - they are all provided as cut-down versions through Busybox. Since these tools are used extensively throughout the firmware, a Busybox upgrade is always at risk of breaking something in the least expected part of the firmware.
The main reason for upgrading Busybox is security, in addition to a wide range of minor bug fixes. Asuswrt-Merlin was running 1.20, and Asus's original firmware is on 1.17.4. We both had various tidbits backported from newer versions, but only a very limited amount of things were updated that way in the past.
I have uploaded some test builds based on the Busybox 1.25.1 upgrade implemented by theMIROn. This is the only change over 380.64 at this time:
https://www.mediafire.com/folder/bj94sbhrh7e49/Test_Builds
If you are willing to give these a test run, please do. I've ran it for over a week myself, everything I tested so far was looking good. Please treat this builds as being experimental for the time being. Be ready to do some troubleshooting if you run into any issue, such as re-testing with 380.64 to compare results.
Pretty much everything will need to be tested over time, but what is the most likely to break is any custom scripts users might have written. AB Solution has already been tested and confirmed to be working properly so far - that's one of the most complex scripts typically found on Asuswrt-Merlin routers so far. I also tested Download Master, which was one of the things that broke back when I upgraded to 1.20.2 a few years ago (I had to revert one specific update to fix it).
The main reason for upgrading Busybox is security, in addition to a wide range of minor bug fixes. Asuswrt-Merlin was running 1.20, and Asus's original firmware is on 1.17.4. We both had various tidbits backported from newer versions, but only a very limited amount of things were updated that way in the past.
I have uploaded some test builds based on the Busybox 1.25.1 upgrade implemented by theMIROn. This is the only change over 380.64 at this time:
https://www.mediafire.com/folder/bj94sbhrh7e49/Test_Builds
If you are willing to give these a test run, please do. I've ran it for over a week myself, everything I tested so far was looking good. Please treat this builds as being experimental for the time being. Be ready to do some troubleshooting if you run into any issue, such as re-testing with 380.64 to compare results.
Pretty much everything will need to be tested over time, but what is the most likely to break is any custom scripts users might have written. AB Solution has already been tested and confirmed to be working properly so far - that's one of the most complex scripts typically found on Asuswrt-Merlin routers so far. I also tested Download Master, which was one of the things that broke back when I upgraded to 1.20.2 a few years ago (I had to revert one specific update to fix it).