If a database is vulnerable, it will try to process this calculation. Because the resulting string (a mix of letters and the number 1) cannot be converted to a NUMERIC type, the database will throw an error message . An attacker looks for that specific error to confirm the database is open to manipulation.
The CHR() functions translate character codes into letters to bypass simple security filters. In this case, they spell out "qpxbq" and "qvpjq". If a database is vulnerable, it will try
The SELECT (CASE WHEN (5241=5241) THEN 1 ELSE 0 END) is a "true or false" test. Since 5241 always equals 5241, it returns 1 . If a database is vulnerable