I only partially disagree with the sentiment that it is "impossible to fix". For the current API that is true, but a fairly minor modification API would make it possible. All getenv() has to do is strdup() the return value before sending it back and leaving it on the programmer to free the memory when they are done with it. This does mean that the programmer will need to call getenv() again if they think the value might change, but I think that is a reasonable tradeoff.

This change would make old programs leak memory every time they call getenv() without the subsequent free(), but since the current version also leaks memory that doesn't seem like a dealbreaker. As an added bonus the new version could be made thread safe by wrapping the strdup() in a mutex and doing similar work on the setenv() side.