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Test For Invalid Data - Mysql Injection Attacks

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Today someone tried to inject some invalid data into a contacts database table.  The data fields are just VARCHARs. Fortunately I had enough checks in there to prevent the insertion.


But I hastily put together the following PHP data checks to try and strengthen the defences.  Are they sufficient?  Is there a better way?  Note: there are no particularly sensitive data in this database but I'd like to prevent any 'bad' data being put into the database table.

function test_for_invalid_data($data)


  // the following are 'needle in haystack' tests - stristr does a case-insensitive check

  if ((stristr($data, 'href') === FALSE) 

    && (stristr($data, 'http') === FALSE)

    && (stristr($data, '<a') === FALSE)

    && (stristr($data, 'link') === FALSE)

    && (stristr($data, 'url') === FALSE)

    && (stristr($data, '</a') === FALSE))

   { // 'needle' strings not found - good!

    return TRUE;



   return FALSE;


Any advice will be most appreciated.



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I think you're thinking of XSS (cross-site scripting), not SQL injection.

To start, I'd recommend doing a YouTube search for "XSS" and "SQL injection", watching a few videos, and then coming back here if you have any questions.


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If you're just looking for characters that might reflect spam or a hack attempt, I'd included "script" and "img". 

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Thank you both for your advice - I will do as you both suggest.


I forgot to mention that I also always use Larry's 'escape-data' process.


Cheers from Oz.

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