Another problem is that it is hard to reason about security in a C program if all environment variables could change at all times. If we are talking about the

Another problem is that it is hard to reason about security in a C program if all environment variables could change at all times. If we are talking about the C application deciding when it wants to rescan the environment that is something different, but if your environment can change potentially before and after you check it this opens you up for a heap of new attacks.