5550'XOR(555*if(now()=sysdate(),sleep(15),0))XOR'Z

It looks like a time‑based blind SQL injection payload. It’s designed to test whether an app is vulnerable and, if so, to cause a deliberate delay that lets an attacker infer information.

What the parts are trying to do (high level)

• 5550' ... XOR'Z: This is likely attempting to break out of a quoted string in a SQL query and inject additional SQL after the quote. The XOR parts are used to shape the injected payload so the overall statement remains syntactically plausible.
• IF(now()=sysdate(), sleep(15), 0): A conditional that, if true, sleeps for 15 seconds; otherwise returns 0.
  • now() and sysdate() are SQL time functions. In MySQL, NOW() is the time at the start of the statement, while SYSDATE() is the time of evaluation. In many cases they are equal within the same second, so the IF condition can evaluate to true, triggering the sleep.
• 555* if(...): Multiplies the result of the IF by 555, which in practice affects the numeric value but, more importantly, serves to keep the payload within the expected syntax of the surrounding query.
• The net effect (in a vulnerable application): If the injection succeeds, the database server will delay its response by about 15 seconds. An attacker can infer true/false or other conditions based on the presence or absence of that delay.

Why this is a concern

• It demonstrates a time-based blind SQL injection technique: the attacker doesn’t see data directly but learns about the database by measuring response times.
• If such an injection is possible, an attacker could gradually extract data or perform unauthorized actions.

Defensive steps (high level)

• Use parameterized queries / prepared statements (no string concatenation of untrusted input).
• Do not rely on input sanitization alone; validate and whitelist inputs.
• Limit database user privileges (least privilege) and disable dangerous functions (e.g., sleep) where feasible.
• Apply web application firewall (WAF) rules and monitor for unusual patterns like time-based delays.
• Keep your database and application frameworks patched; review error messages that might reveal SQL structure.

If you’re studying for an exam, key takeaways to recognize a payload like this

• Quoted string termination followed by injected SQL (closing a literal).
• Use of time-based functions (e.g., SLEEP) to cause delays.
• Conditional logic to trigger the delay only in certain circumstances (IF, NOW vs SYSdate).
• ASCII/obfuscation attempts (like XOR) to bypass simple filters or to maintain syntax.

If you want, I can walk through a safe, conceptual example in a controlled lab setup (no real systems involved) to illustrate how a time-based blind SQL injection test works and how to defend against it.