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Re: PHP filter function against SQL injections
From: jeffrey rivero <jeffr76 () yahoo com>
Date: Fri, 09 Feb 2007 09:19:37 -0500

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.

consider

$sSql .= " where a = ". '$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:
Hello
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:
Hi

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 () downtowndevelopmentplan com 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:
 >
 > http://www.securityfocus.com/infocus/1768
 >
 > 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?

Greetings


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

Regards,
Koen

On 2/7/07, Kellox <kellox () mymail ch> 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
function?
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