A colleague of mine(Aleks) forwarded me a russian presentation on exploiting SQL Injection:
http://devteev.blogspot.com/2009/10/advanced-sql-injection-lab-full-pack.html
Of all the slides, i particular liked the one in which the author demonstrates that if the mysql error messages have been enabled (using mysql_error() function), then it is possible to retrieve the data from the back-end database using the ExtractValue() function:
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>SELECT 1 AND ExtractValue(1, CONCAT(0x5c, (SELECT @@VERSION)))
produces:
Error Code : 1105
XPATH syntax error: '5.1.44-community'
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This should not be confused with the php errors. While the php errors are usually enabled its not "very" common to see developers printing the mysql errors using mysql_error() function. However, its still good to know and could sometimes come handy.
Overall, very nice presentation.