Suggestion on how to eliminate Cross-site-scripting (XSS) bugs for good.

Hi all!

I am working on Yapcom ( http://yapcom.pti.co.il/ ) which is a Perl 
application that makes use of CGI::Application and HTML::Template. Now we had 
problems of Cross Site Scripting (XSS) in the past and I came up with this 
suggestion to hopefully eliminate them, that is based on the idea that it 
should be hard to output unescaped strings as is:

The HTML::Template documentation for TMPL_VAR:

http://search.cpan.org/~samtregar/HTML-Template-2.8/Template.pm#TMPL_VAR

Reads:

<<<<
Optionally you can use the "ESCAPE=HTML" option in the tag to indicate that 
you want the value to be HTML-escaped before being returned from output (the 
old ESCAPE=1 syntax is still supported). This means that the ", <, >, and & 
characters get translated into &quot;, &lt;, &gt; and &amp; respectively. 
This is useful when you want to use a TMPL_VAR in a context where those 
characters would cause trouble. Example:
>>>>

Now what I want is to sub-class HTML::Template so we'll always have to 
use "ESCAPE=HTML". If we want to override it we'll need to do the following:

1. Wrap the string in a special object:

<<<<<
my $string_to_pass = "<h1>Hello</h1>";

my $string_to_pass_as_obj = YAPC::Template::PassThru->new($string_to_pass);
>>>>>

2. Explicitly unlock the object:

<<<<<<
$string_to_pass_as_obj->unlock("unlock");
>>>>>>

Note that unlock returns undef.

3. Add a special parameter to TMPL_VAR:

<<<<<<
<TMPL_VAR NAME="string_to_pass" PASSTHRU="1">
>>>>>>

-----------------

If we pass a simple string then we can only use the TMPL_VAR with 
ESCAPE="HTML" added. We can also use ESCAPE="HTML" on an unlocked object.

---------------------------

My question is: can this be already done with H::T? If not, I guess I'll work 
on a sub-class of H::T to do such a thing, unless someone can come up with a 
better idea.

Regards,

        Shlomi Fish

---------------------------------------------------------------------
Shlomi Fish      shlomif@xxxxxxxxxxx
Homepage:        http://www.shlomifish.org/

Chuck Norris wrote a complete Perl 6 implementation in a day but then
destroyed all evidence with his bare hands, so no one will know his secrets.

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