Matthew Dalton wrote:
> > system("graph -L 'Mono-molecular Reaction' -X Time -Y
> > 'Concentration' /tmp/data >| /tmp/temp.meta");
> > system("plot -T gif /tmp/temp.meta >| /tmp/order1.gif");
>
> Is there a security risk with a call such as this?
> You're not supposed to put system calls in cgi for security reasons, but
> does that rule include situations such as this where the command is
> constant?
You are not supposed to call a script or program
with parameters that originate from an external source
such as form variables from an HTML form on the web.
Why?
Because this:
system("cat $parameter")
becomes this:
system("cat /etc/passwd; rm -rf /tmp/*")
when a savvy user types "/etc/passwd; rm -rf /tmp/*"
into the text box that winds up in your $parameter variable.
Perl has a TAINT (-T) option to disallow such calls unless you
inspect and 'fix' $parameter to be safe from such exploits.
...................................
Michael Lake wrote:
> I am doing this:
i.e. you have writtten:
(1) script that displays a form to return a GIF image
from a temp directory, generated on the fly
re-write this as follows:
(1) script that displays a page that contains an image
tag direct to the CGI:
<h1>Kinetics Image</h1>
<img src="http://whatever/cgi-bin/genimage?a=123456789">
Note: try to keep make "123456789" a different number
each time you generate this page -- should stop caching effects
(2) script that generates a kinetics image on the fly,
returning a GIF header, called genimage
system("graph -L 'Mono-molecular Reaction' -X Time -Y
'Concentration' /tmp/data >| /tmp/temp.meta");
system("plot -T gif /tmp/temp.meta >| /tmp/order1.gif");
:
:
# generate header and content
my $size = -s "/tmp/order1.gif";
print $q->header(-type=>'image/gif',
-content-length=>$size,
-expires=>'+30s',
-pragma=>'no-cache',
-cache-control=>'no-cache');
open(GIF,"/tmp/order1.gif") || die;
print join "",<GIF>;
close GIF;
I haven't tested this code. You may have to make modifications
to get it to work properly and, as always, YMMV.
--
Rick Welykochy || Praxis Services Pty Limited
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