Project Discovery’s mapcidr had a bug when converting IP addresses. The “-ip-format” flag did not properly work for one of the cases. For example, echo '127.0.0.1' | mapcidr -ip-format 5 would incorrectly return the integer representation or decimal value 281472812449793 , when it should have returned the decimal value 2130706433 . The problem could be seen in the Go function here which uses functionality imported from the math library . func IPToInteger(ip net.IP) (*big.Int, int, error) { val := &big.Int{} val.SetBytes([]byte(ip)) if len(ip) == net.IPv4len { return val, 32, nil //nolint } else if len(ip) == net.IPv6len { return val, 128, nil //nolint } else { return nil, 0, fmt.Errorf("unsupported address length %d", len(ip)) The function was easily fixed by removing the early "setBytes" value and rewriting it to correctly set the bytes conditionally for each if-statement, depending on the IP type. func IPToInteger(ip net.IP) (*big....