the same issue reproduced on Big Sur 11.2.1 MacBook 15 2015 sudo /usr/libexec/ApplicationFirewall/socketfilterfw --getappblocked /usr/bin/nc The file path you specified is invalid or sudo /usr/libexec/ApplicationFirewall/socketfilterfw --add /usr/local/bin/mosh-server The file path you specified is invalid in general, every operation with a path gets this result