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Protect against SQL Injection by whitelisting

OK, admittedly the best practice for guarding against SQL Injection attacks is to white-list acceptable characters. However, given that knowledge is power, is there a comprehensive list of special characters (such as the single-quote or double-hyphen) available for SQL Server? I have done a ton of searches and can't seem to find one (I did find the reserved words).

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SQL is such a powerful language (some would say too powerful) that there isn't a really good list to use for blacklisting. You're right on the money, that whitelisting is your first line of defense. I always like to use a RegEx function to filter all my user provided input. If the data passes the RegEx, then I pass it through a very simple blacklist function as a just-in-case. To date, I haven't seen anything in any application I've written that ever fired off the blacklist function because the whitelist is much more powerful. Whitelisting isn't as hard as you may think; a bunch of examples of RegEx in ASP and PHP abound and you can get really great examples of RegEx strings at www.regexlib.com.

This was first published in March 2007

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