Advisory Title: CGI.pm vulnerable to Cross-site Scripting. Release Date: July 19 2003
Application: CGI.pm - which is by default included in many common Perl distributions.
Platform: Most platforms. Tested on Apache and IIS.
Severity: Effects scripts which make use of start_form()
Author: Obscure^ [ email@example.com ]
Vendor Status: first informed on 30th April 2003 Although the author told EoS that he will be releasing a fix within a week from his last correspondence (May15), no fix is out yet on his website.
(extracted from http://stein.cshl.org/WWW/software/CGI/)
This perl 5 library uses objects to create Web fill-out forms on the fly and to parse their contents. It provides a simple interface for parsing and interpreting query strings passed to CGI scripts. However, it also offers a rich set of functions for creating fill-out forms. Instead of remembering the syntax for HTML form elements, you just make a series of perl function calls. An important fringe benefit of this is that the value of the previous query is used to initialize the form, so that the state of the form is preserved from invocation to invocation. .
CGI.pm has the ability to create forms by making use of the start_form() function. The developer/perl scripter can also makes use of start_multipart_form() which relies on start_form() and is therefore vulnerable to the same issue. When the action for the form is not specified, it is given the value of $self->url(-absolute=>1,-path=>1) - which means that when the url is something like the following :
.. the form becomes <form action="http://host/script.pl">some text<!-- " >
In such case, it is possible to exploit this issue to launch a Cross Site Scripting attack.
$q = new CGI; print $q->header; print $q->start_html('CGI.pm XSS'); print $q->start_form(); print $q->end_form(); print $q->end_html;
I fixed my CGI.pm by adding the following code at line 1537
$action =~ s/\"/\%22/g;
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