More information about the exploit and affected mods and solutions can be found at. The best course of action currently if you play older modpacks on 1.7/1.12 is to simply not join any public servers unprotected and to add this mod to your instances to protect yourself from the exploit. Due to the nature of this being a remote code execution exploit, any attacker on the same server as you could've run any code on your computer, so as such there's no way to tell if you've been affected or what code was run. If you play singleplayer only you don't have anything to worry about, only if you play online on public servers. The scope at the moment seems to mostly affect mods on 1.7 and 1.12 but may also occur on other Minecraft versions, there is still work going on to find a full list of mods and affected versions. This is an RCE which allows bad actors to run code remotely on your computer when connected on the same server as them.

Unfortunately there is another exploit going around the modded Minecraft community at the moment.

Minecraft modded servers launcher