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Re^5: use of print f and sprint f

by blokhead (Monsignor)
on Nov 10, 2004 at 16:50 UTC ( #406717=note: print w/ replies, xml ) Need Help??

in reply to Re^4: use of print f and sprint f
in thread use of print f and sprint f

cannot be exploited
Depends on what you mean, I guess.. Check out the perldoc, and look at the %n format. You can set values.
%n special: *stores* the number of characters output so far into the next variable in the parameter list
Suppose I have the following code:
my $name = ...; ## from user input my $amount = ...; printf "$name : \$%.02f\n", $amount; # instead of # printf "%s : \$%.02f\n", $name, $amount;
Now, if a clever hacker goes in and inputs
$name = (" " x 5000) . "%n";
then after the code runs, $amount will be set to 5000. This is a pretty rare set of circumstances, but still something to watch out for.

Update: see also Re: $#="%c"; possible bug


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