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Re: Sanitising input [message #172112 is a reply to message #172089]

Mon, 31 January 2011 01:17

Norman Peelman
Messages: 126
Registered: September 2010

Karma:

Senior Member

Denis McMahon wrote:
> On 30/01/11 14:09, Mad Hatter wrote:
>
>> I'm writing a simple script which will take a users input, save it to a
>> mysql database and then display it. I'm going to use htmlentities() to
>> clean things up which I hope will stop basic attacks but how else should I
>> sanitise my input?
>
> strings - use mysql_real_escape_string before using the string value as
> data in an sql statement, eg:
>
> $the_text = $_POST['text_field'];
> $the_text = trim($the_text);
> $the_text = str_replace($old,$new,$the_text);
> // maybe do some additional stuff to $the_text here
> $safe_text = mysql_real_escape_string($the_text);
> $qry = "update table set field = '$safe_text' where otherfield = '$keyval'";
> mysql_query($qry);
>
> floats and ints, use floatval or intval to read them from the post or
> get array:
>
> $the_float = floatval($_POST['number_field']);
> $the_int = inttval($_POST['number_field']);
>
> dates & times, if you allow these to be entered as text fields, you
> might get meaningful data with parse_date or strtotime, but it might be
> better to use numbers and handle them as ints, or select elements.
>
> Note that you can absolutely never assume that the data you receive will
> bear any connection with your web page. It is trivial for an attacker to
> view your form html, and to generate his own form that calls your form
> handler with whatever data he desires to send in every form element.
>
> The fact that your select element for year has values from "2001" to
> "2020" doesn't stop an attacker sending:
>
> "';;drop *;;"
>

To the best of my knowledge, the PHP/MySQL library doesn't allow more
than one sql statement in the same query.

> or a base 64 encoded image file, or anything else at all, so you need to
> write your scripts so that they check everything and only accept data
> that they recognise.
>
> Rgds
>
> Denis McMahon

--
Norman
Registered Linux user #461062
-Have you been to www.php.net yet?-

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[Message index]

		Sanitising input By: Mad Hatter on Sun, 30 January 2011 14:09
		Re: Sanitising input By: Michael Fesser on Sun, 30 January 2011 15:00
		Re: Sanitising input By: Denis McMahon on Sun, 30 January 2011 16:35
		Re: Sanitising input By: Norman Peelman on Mon, 31 January 2011 01:17
		Re: Sanitising input By: Captain Paralytic on Mon, 31 January 2011 11:51
		Re: Sanitising input By: Norman Peelman on Mon, 31 January 2011 23:39
		Re: Sanitising input By: Denis McMahon on Tue, 01 February 2011 00:53
		Re: Sanitising input By: Norman Peelman on Tue, 01 February 2011 11:26
		Re: Sanitising input By: Denis McMahon on Mon, 31 January 2011 12:05
		Re: Sanitising input By: P E Schoen on Sun, 30 January 2011 19:47
		Re: Sanitising input By: Felix Saphir on Sun, 30 January 2011 19:55
		Re: Sanitising input By: Ross McKay on Sun, 30 January 2011 21:39
		Re: Sanitising input By: Jerry Stuckle on Sun, 30 January 2011 21:50
		Re: Sanitising input By: Ross McKay on Mon, 31 January 2011 03:43
		Re: Sanitising input By: Jerry Stuckle on Mon, 31 January 2011 04:12
		Re: Sanitising input By: Ross McKay on Mon, 31 January 2011 05:01
		Re: Sanitising input By: Jerry Stuckle on Mon, 31 January 2011 05:10
		Re: Sanitising input By: Ross McKay on Mon, 31 January 2011 05:38
		Re: Sanitising input By: Jerry Stuckle on Mon, 31 January 2011 12:51
		Re: Sanitising input By: Sherm Pendley on Sun, 30 January 2011 22:18
		Re: Sanitising input By: Ross McKay on Mon, 31 January 2011 03:52
		Re: Sanitising input By: Sherm Pendley on Mon, 31 January 2011 05:23

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