{keyword}) Union All Select Null,null,null,null,null,null# -

: Only allow expected characters and formats.

: In MySQL, the hash symbol marks the rest of the line as a comment . This effectively deletes any remaining parts of the original developer's code (like a trailing WHERE clause or a closing quote) that would otherwise cause a syntax error. Why This Matters

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 {KEYWORD}) UNION ALL SELECT NULL,NULL,NULL,NULL,NULL,NULL#

: This treats user input as data, not as executable code.

: 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. : Only allow expected characters and formats

If this payload successfully returns a blank page instead of an error, it confirms to a tester that the application is vulnerable. From there, they can replace the NULL s with commands to extract sensitive data, such as: Usernames and passwords. Database version and configuration details. The entire contents of specific tables. How to Prevent It

: This is a common reconnaissance technique. An attacker uses NULL values to determine the exact number of columns returned by the original query. If the number of NULL s doesn't match the original column count, the database will usually throw an error. By adding or removing NULL s, an attacker can find the correct structure. Why This Matters The string you provided is

: Most modern frameworks like Hibernate or Entity Framework handle this protection automatically.