{keyword}) Union All Select Null,null,null,null,null-- Zkhd «CONFIRMED»

: The number of NULL values (5 in this case) does not match the number of columns in the original table.

: This is likely a random string or a "signature" used by a vulnerability scanner (like Burp Suite or sqlmap) to track if the payload was successfully reflected in the application's response. {KEYWORD}) UNION ALL SELECT NULL,NULL,NULL,NULL,NULL-- ZkhD

: This command combines the result set of the original query with a new set of data. UNION ALL is used instead of UNION because it is often faster and does not remove duplicates, which can be useful for certain types of data extraction. : The number of NULL values (5 in

: This part attempts to break out of the existing SQL query structure. The closing parenthesis ) is used to "close" a likely function or subquery in the application's original code. UNION ALL is used instead of UNION because

: The attacker uses a specific number of NULL values to match the number of columns in the original query's SELECT statement. NULL is used because it is compatible with almost any data type (strings, integers, dates), maximizing the chance that the injected query will succeed.