A security hole

[Johannes Heuft]

In general: using system(3) or popen(3) inside a set-uid-on-exec
program is a severe security violation. Please believe guys
how know about it. If I would tell why, everybody could crack a
SVR2 within a four-line shell script! AT&T did a lot for
fixing this security hole in SVR3.*

For the same reason set-uid shell scripts should be outlawed (in BSD4.*).
Note, that getcwd(3) still calls popen("/bin/pwd" ...). Use getpwd()
if this routine is available.