XSS problem

Hi,

I have never really been aware of this before, but we have a client who has told us our forms are vunerable to attacks. So we have to change them. I found a function which allows us to fix this problem, but we are unsure how to implement it into our code. Here is our script:

[code=php]
<?
//# Include the connections script to make a database connection.

include(“inc/connect.inc”);

//# The form should post to itself.
if ( $_POST[‘submit’] ) {

$valid = 1;

//# The fields all follow this patern.
//# If you do not require an error check for a field then just use the
//# post field method and not the error check method

$Tabletop_Microscope = $_POST[‘Tabletop_Microscope’];

$Name = $_POST[‘Name’];
if ( empty($Name) ) {
$valid = 0;
$Name_error = ‘<b><font face=”Tahoma” color=”#FF0000″ size=4><span class=”style57″>Please Enter your Name</span></font></b>’;
}

$Company_Name = $_POST[‘Company_Name’];
if ( empty($Company_Name) ) {
$valid = 0;
$Company_Name_error = ‘<b><font face=”Tahoma” color=”#FF0000″ size=4><span class=”style57″>Please Enter your Company Name</span></font></b>’;
}

$Telephone = $_POST[‘Telephone’];
if ( empty($Telephone) ) {
$valid = 0;
$Telephone_error = ‘<b><font face=”Tahoma” color=”#FF0000″ size=4><span class=”style57″>Please Enter your Telephone Number</span></font></b>’;
}

$Email = $_POST[‘Email’];
$Web_Site_Comments = $_POST[‘Web_Site_Comments’];

$antispambox = $_POST[‘antispambox’];
if ($antispambox == ‘73634’) {}
else
{
$valid = 0;
$antispambox_error = ‘<b><font face=”Tahoma” color=”#FF0000″ size=4><span class=”style57″>Please Enter the Numbers as shown in bold</span></font></b>’;
}

// End of error checking.

if ( $valid == 1 )
{
// In testing, if you get an Bad referer error
// comment out or remove the next three lines
if (strpos($_SERVER[‘HTTP_REFERER’], $_SERVER[‘HTTP_HOST’])>7 ||
!strpos($_SERVER[‘HTTP_REFERER’], $_SERVER[‘HTTP_HOST’]))
die(“Bad referer”);
$msg=”This is the information received from the Spectroscopy Enquiry Form.:nn”;
foreach($_POST as $key => $val){
if (is_array($val)){
$msg.=”Item: $keyn”;
foreach($val as $v){
$v = stripslashes($v);
$msg.=”***$vn”;
}
} else {
$val = stripslashes($val);
$msg.=”$key: $valn”;
}
}
$recipient=”*****”;
$subject=”Enquiry Form”;
error_reporting(0);
if (mail($recipient, $subject, $msg)){
echo nl2br($input);
} else
echo “An error occurred and the message could not be sent.”;

header(“Location: thanks.php”);
exit;
}
}
?>
[/code]

And here is the function. Now can someone tell me if we have to run this function on every field in the form???

[code=php]
function RemoveXSS($val) {
// remove all non-printable characters. CR(0a) and LF(0b) and TAB(9) are allowed
// this prevents some character re-spacing such as <javascript>
// note that you have to handle splits with n, r, and t later since they *are* allowed in some inputs
$val = preg_replace(‘/([x00-x08][x0b-x0c][x0e-x20])/’, ”, $val);

// straight replacements, the user should never need these since they’re normal characters
// this prevents like <IMG SRC=&#X40&#X61&#X76&#X61&#X73&#X63&#X72&#X69&#X70&#X74&#X3A&#X61&#X6C&#X65&#X72&#X74&#X28&#X27&#X58&#X53&#X53&#X27&#X29>
$search = ‘abcdefghijklmnopqrstuvwxyz’;
$search .= ‘ABCDEFGHIJKLMNOPQRSTUVWXYZ’;
$search .= ‘1234567890!@#$%^&*()’;
$search .= ‘~`”;:?+/={}[]-_|’\’;
for ($i = 0; $i < strlen($search); $i++) {
// ;? matches the ;, which is optional
// 0{0,7} matches any padded zeros, which are optional and go up to 8 chars

// &#x0040 @ search for the hex values
$val = preg_replace(‘/(&#[x|X]0{0,8}’.dechex(ord($search[$i])).’;?)/i’, $search[$i], $val); // with a ;
// &#00064 @ 0{0,7} matches ‘0’ zero to seven times
$val = preg_replace(‘/(&#0{0,8}’.ord($search[$i]).’;?)/’, $search[$i], $val); // with a ;
}

// now the only remaining whitespace attacks are t, n, and r
$ra1 = Array(‘javascript’, ‘vbscript’, ‘expression’, ‘applet’, ‘meta’, ‘xml’, ‘blink’, ‘link’, ‘style’, ‘script’, ’embed’, ‘object’, ‘iframe’, ‘frame’, ‘frameset’, ‘ilayer’, ‘layer’, ‘bgsound’, ‘title’, ‘base’);
$ra2 = Array(‘onabort’, ‘onactivate’, ‘onafterprint’, ‘onafterupdate’, ‘onbeforeactivate’, ‘onbeforecopy’, ‘onbeforecut’, ‘onbeforedeactivate’, ‘onbeforeeditfocus’, ‘onbeforepaste’, ‘onbeforeprint’, ‘onbeforeunload’, ‘onbeforeupdate’, ‘onblur’, ‘onbounce’, ‘oncellchange’, ‘onchange’, ‘onclick’, ‘oncontextmenu’, ‘oncontrolselect’, ‘oncopy’, ‘oncut’, ‘ondataavailable’, ‘ondatasetchanged’, ‘ondatasetcomplete’, ‘ondblclick’, ‘ondeactivate’, ‘ondrag’, ‘ondragend’, ‘ondragenter’, ‘ondragleave’, ‘ondragover’, ‘ondragstart’, ‘ondrop’, ‘onerror’, ‘onerrorupdate’, ‘onfilterchange’, ‘onfinish’, ‘onfocus’, ‘onfocusin’, ‘onfocusout’, ‘onhelp’, ‘onkeydown’, ‘onkeypress’, ‘onkeyup’, ‘onlayoutcomplete’, ‘onload’, ‘onlosecapture’, ‘onmousedown’, ‘onmouseenter’, ‘onmouseleave’, ‘onmousemove’, ‘onmouseout’, ‘onmouseover’, ‘onmouseup’, ‘onmousewheel’, ‘onmove’, ‘onmoveend’, ‘onmovestart’, ‘onpaste’, ‘onpropertychange’, ‘onreadystatechange’, ‘onreset’, ‘onresize’, ‘onresizeend’, ‘onresizestart’, ‘onrowenter’, ‘onrowexit’, ‘onrowsdelete’, ‘onrowsinserted’, ‘onscroll’, ‘onselect’, ‘onselectionchange’, ‘onselectstart’, ‘onstart’, ‘onstop’, ‘onsubmit’, ‘onunload’);
$ra = array_merge($ra1, $ra2);

$found = true; // keep replacing as long as the previous round replaced something
while ($found == true) {
$val_before = $val;
for ($i = 0; $i < sizeof($ra); $i++) {
$pattern = ‘/’;
for ($j = 0; $j < strlen($ra[$i]); $j++) {
if ($j > 0) {
$pattern .= ‘(‘;
$pattern .= ‘(&#[x|X]0{0,8}([9][a][b]);?)?’;
$pattern .= ‘|(&#0{0,8}([9][10][13]);?)?’;
$pattern .= ‘)?’;
}
$pattern .= $ra[$i][$j];
}
$pattern .= ‘/i’;
$replacement = substr($ra[$i], 0, 2).'<x>’.substr($ra[$i], 2); // add in <> to nerf the tag
$val = preg_replace($pattern, $replacement, $val); // filter out the hex tags
if ($val_before == $val) {
// no replacements were made, so exit the loop
$found = false;
}
}
}
return $val;
}
[/code]

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