I am tring to make my PHP as secure as possible, and the two main things I am trying to avoid are
This is the script I got against mySQL Injections:
function make_safe($variable) {
$variable = mysql_real_escape_string(trim($variable));
return $variable; }
http://www.addedbytes.com/writing-secure-php/writing-secure-php-1/
Against XSS, I found this:
$username = strip_tags($_POST['username']);
Now I want to unite the two into a single function. Would this be the best way to do so? :
function make_safe($variable) {
$variable = strip_tags(mysql_real_escape_string(trim($variable)));
return $variable; }
Or does the mysql_real_escape_string already prevent XSS? And lastly, is there anything else that I could add into this function to prevent other forms of hacking?
This function:
function make_safe($variable)
{
$variable = strip_tags(mysql_real_escape_string(trim($variable)));
return $variable;
}
Will not work
SQL injection and XSS are two different beasts. Because they each require different escaping you need to use each escape function strip_tags
and mysql_real_escape_string
separatly.
Joining them up will defeat the security of each.
Use the standard mysql_real_escape_string()
when inputting data into the database.
Use strip_tags()
when querying stuff out of the database before outputting them to the screen.
Why combining the two function is dangerous
From the horses mouth: http://php.net/manual/en/function.strip-tags.php
Because strip_tags() does not actually validate the HTML, partial or broken tags can result in the removal of more text/data than expected.
So by inputting malformed html into a database field a smart attacker can use your naive implementation to defeat mysql_real_escape_string()
in your combo.