[steamrolled]

The main reason system() exists is that people want to execute shell commands; some confused novice developers might mix it up with execl(), but this is not a major source of vulnerabilities. The major source of vulnerabilities is "oh yeah, I actually meant to execute shell".

So if you just take away the libcall, people will make their own version by just doing execl() of /bin/sh. If you want this to change, I think you have to ask why do people want to do this in the first place.

And the answer here is basically that because of the unix design philosophy, the shell is immensely useful. There are all these cool, small utilities and tricks you can use in lieu of writing a lot of extra code. On Windows, command-line conventions, filesystem quirks, and escaping gotchas are actually more numerous. It's just that there's almost nothing to call, so you get fewer bugs.

The most practical way to make this class of bugs go away is to make the unix shell less useful.

[rcxdude]

most calls to system() that I've seen could be replaced with exec without much difficulty. There's relatively few that actually need the shell functionality.

[oguz-ismail]

system() involves fork()ing, setting up signal handlers, exec()ing and wait()ing. You won't be replacing it with exec, most of the time you'll be reimplementing it for absolutely no reason.