FAQ 9.14 How do I make sure users can't enter values into a form that cause my CGI script ...

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9.14: How do I make sure users can't enter values into a form that cause my CGI
script to do bad things?

    (contributed by brian d foy)

    You can't prevent people from sending your script bad data. Even if you
    add some client-side checks, people may disable them or bypass them
    completely. For instance, someone might use a module such as "LWP" to
    access your CGI program. If you want to prevent data that try to use SQL
    injection or other sorts of attacks (and you should want to), you have
    to not trust any data that enter your program.

    The perlsec documentation has general advice about data security. If you
    are using the "DBI" module, use placeholder to fill in data. If you are
    running external programs with "system" or "exec", use the list forms.
    There are many other precautions that you should take, too many to list
    here, and most of them fall under the category of not using any data
    that you don't intend to use. Trust no one.


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