C system() function vulnerability
If this is actually in live code somewhere, then whomever wrote it should be forced to write I will never call system on tainted user input again 1 googol times with a dull pencil.  Yes.  As written, this code contains an exploit.  Here's a simple example.

tmp$ cat foo.c
#include &lt;stdlib.h&gt;
#include &lt;stdio.h&gt;

int
main() {
    char *user = getenv("USER");
    char buffer[4096];
    if (user) {
        snprintf(buffer, sizeof buffer, "/bin/echo %s", user);
        printf("running %s\n", buffer);
        system(buffer);
    }
    return 0;
}
tmp$ gcc foo.c
tmp$ mkdir /tmp/xxx
tmp$ ls -ld /tmp/xxx
drwxr-xr-x  2 daveshawley  users  68 Nov 30 22:25 /tmp/xxx/
tmp$ USER='foo; rm -fr /tmp/xxx' ./a.out
running /bin/echo foo; rm -fr /tmp/xxx
foo
tmp$ ls -ld /tmp/xxx
ls: /tmp/xxx: No such file or directory
tmp$