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    <p>I sanitize my user data much like Radu...</p> <ol> <li><p>First client-side using both regex's and taking control over allowable characters input into given form fields using javascript or jQuery tied to events, such as onChange or OnBlur, which removes any disallowed input before it can even be submitted. Realize however, that this really only has the effect of letting those users in the know, that the data is going to be checked server-side as well. It's more a warning than any actual protection.</p></li> <li><p>Second, and I rarely see this done these days anymore, that the first check being done server-side is to check the location of where the form is being submitted from. By only allowing form submission from a page that you have designated as a valid location, you can kill the script BEFORE you have even read in any data. Granted, that in itself is insufficient, as a good hacker with their own server can 'spoof' both the domain and the IP address to make it appear to your script that it is coming from a valid form location.</p></li> <li><p>Next, and I shouldn't even have to say this, but always, and I mean <strong>ALWAYS</strong>, run your scripts in taint mode. This forces you to not get lazy, and to be diligent about step number 4.</p></li> <li><p>Sanitize the user data as soon as possible using well-formed regexes appropriate to the data that is expected from any given field on the form. Don't take shortcuts like the infamous '<em>magic horn of the unicorn</em>' to blow through your taint checks... or you may as well just turn off taint checking in the first place for all the good it will do for your security. That's like giving a psychopath a sharp knife, bearing your throat, and saying 'You really won't hurt me with that will you".</p> <p>And here is where I differ than most others in this fourth step, as I only sanitize the user data that I am going to actually USE in a way that may present a security risk, such as any system calls, assignments to other variables, or any writing to store data. If I am only using the data input by a user to make a comparison to data I have stored on the system myself (therefore knowing that data of my own is safe), then I don't bother to sanitize the user data, as I am never going to us it a way that presents itself as a security problem. For instance, take a username input as an example. I use the username input by the user only to check it against a match in my database, and if true, after that I use the data from the database to perform all other functions I might call for it in the script, knowing it is safe, and never use the users data again after that.</p></li> <li><p>Last, is to filter out all the attempted auto-submits by robots these days, with a 'human authentication' system, such as Captcha. This is important enough these days that I took the time to write my own 'human authentication' schema that uses photos and an input for the 'human' to enter what they see in the picture. I did this because I've found that Captcha type systems really annoy users (you can tell by their squinted-up eyes from trying to decipher the distorted letters... usually over and over again). This is especially important for scripts that use either SendMail or SMTP for email, as these are favorites for your hungry spam-bots.</p></li> </ol> <p>To wrap it up in a nutshell, I'll explain it as I do to my wife... your server is like a popular nightclub, and the more bouncers you have, the less trouble you are likely to have in the nightclub. I have two bouncers outside the door (client-side validation and human authentication), one bouncer right inside the door (checking for valid form submission location... 'Is that really you on this ID'), and several more bouncers in close proximity to the door (running taint mode and using good regexes to check the user data).</p> <p>I know this is an older post, but I felt it important enough for anyone that may read it after my visit here to realize their is no '<em>magic bullet</em>' when it comes to security, and it takes all these working in conjuction with one another to make your user-provided data secure. Just using one or two of these methods alone is practically worthless, as their power only exists when they all team together.</p> <p>Or in summary, as my Mum would often say... 'Better safe than sorry".</p>
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    1. POWhen is it Best to Sanitize User Input?
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    1. COthanks :) for sharing. I liked the 2 point. i.e. checking the source before form submission.
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      1. USGaurav Sharma
    2. COLocking out blind users is not best practice.
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    3. COUpdate just made it fabulous.
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      1. USYour Common Sense
 

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