Re: XSS in JAB Guest Book

["Steven M. Christey" <coley@xxxxxxxxx>]

>function invalideregtest($input)
>
>script just check $topic by invalideregtest function

I think this function just *tries* to check inputs, but doesn't
succeed.  Did you do any live testing using $topic ?

We should expect to see more erroneous cleansing/checking functions as
programmers attempt to implement security in their products.

>       $checkcount = 0;

This matters later on.

>       //$exinput = str_split($input);
>       $countname = count($exinput);

Since the assignment of $exinput is commented out, the variable is
undefined.  So, $countname is set to 0.

(This was probably commented out because the function doesn't exist in
PHP 4.)

>       for($i=0; $i<$countname; $i++)
>       {

Since $countname is 0, this loop is not entered.

>  if($checkcount != 0)
>  {
>       $input = "no";
>  }
>       else
>  {
>       $input = "yes";
>  }

Since $checkcount is 0, the function always returns "yes", meaning
"the input looks valid to me."

  <SCRIPT>abc</SCRIPT> === yes

  ABCDE GHIF AKLSM === yes

  ABCDEGHIFAKLSM === yes

There might be other logic errors in the function, but this is the
most obvious one.

- Steve