Re: PHP filter function against SQL injections

what if a must be an integer and not a string ?

Kellox wrote:
well, that does only work if the variable is not included between two single quotes.


$sSql .= " where a = ". '$var';

in your code snippet. if you would inject or 1=1 in this case, the string would be

where a = 'or 1=1', which actually is a string but not a sql command.

jeffrey rivero wrote:
Good Questions
ok for the
1.Single and double-quotes will be escaped by the function call mysql_escape_string().
yep but what i am passing does not have " or ' in them think more like or 1 = 1 and assume that your var is a number
so the injections would look like

$sSql = "select a,b,c ";
$sSql .= "from Table_1";
$sSql .= " where a = ".$var;
now if $var was lets say "1 or 1 = 1"
your resulting injection string would be
select a,b,c from Table_1 where a = 1 or 1 = 1
which might now be what you want

2. union injection ??
3. not sure will a post command still do a url encode ?? anyone ?

Kellox wrote:

Thx for your information so far.

Jeffrey Rivero wrote:
> how about something like
> " or 1 = 1"
> ??

Single and double-quotes will be escaped by the function call mysql_escape_string().

jeff@xxxxxxxxxxxxxxxxxxxxxxxxxxx wrote:
> Don't forget that the best way to sanitize incoming data is to only allow
> known-good input. Attempting to filter against a list of bad characters has
> historically proven itself futile. Rewrite your function to only allow the
> characters that your application expects.
> -Jeff

Actually I always use your recommended whitelist approach. but since this filter function is part of a review I'm doing at the moment, I was asking the question about a possible SQL injection attack.

Pete Pinter wrote:
> Won't hex encoded strings get through? You might want to check out this
> link:
> Cheers,
> /p2

As I can see hexencoded strings will also be filtered by the function mysql_escape_string(). For example %27 will be converted into the ASCII-character ' and then it will be escaped by \ resulting it into \'. So hexencoded strings can't bypass this filter, can they?


Koen Bossaert wrote:
You probably also don't want * and %.
You can also make use of prepared statements or stored procedures
against SQL Injection.


On 2/7/07, Kellox <kellox@xxxxxxxxx> wrote:
hi everyone!

i was just wondering if this filter function written in php is safe against
sql injections:

function filter($string) {
$replace = "";
$search = array(">", "<", "|", ";");
$result = mysql_escape_string( str_replace($search, $replace, $string));
return $result;

or could anyone imagine an sql injection attack which bypasses this filter