The string you provided is a specific used to test for vulnerabilities in a database. It is designed to trick a web application into running a second, unauthorized query and appending the results to the original one. Breakdown of the Payload
: Only allow expected characters and formats. {KEYWORD}) UNION ALL SELECT NULL,NULL,NULL,NULL,NULL,NULL#
: This part attempts to "break out" of the existing SQL command. The closing parenthesis ) is used to close a function or a nested query that the developer originally intended. The string you provided is a specific used
To protect your application from this type of attack, you should avoid building queries using simple string concatenation. Instead, use: : This part attempts to "break out" of
: This is the core of the attack. The UNION operator combines the results of two or more SELECT statements into a single result set. ALL ensures that duplicate rows are kept.