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

This looks like a time-based blind SQL injection payload. It’s designed to cause a delay (sleep) on the database server when a condition evaluates to true, allowing an attacker to infer information by measuring response times.

What the parts mean (at a high level)

• 5550' ... 'Z: This pattern is trying to break out of a string literal in a vulnerable SQL query. If a query is something like ... WHERE column = 'input', an attacker can close the quote and inject more SQL.
• XOR( ... ) XOR: In MySQL, XOR is a boolean operator. Here it’s used to append a new boolean expression into the SQL without obviously breaking syntax, helping evade simple checks.
• 555*if(now()=sysdate(),sleep(15),0):
  • if(cond, then, else) is a conditional expression.
  • now() and sysdate() are time-related functions. In MySQL, the equality now() = sysdate() is used as a condition that is satisfied only when the two timestamps line up in the moment the expression is evaluated.
  • sleep(15) makes the server pause for 15 seconds if the condition is true.
  • 0 is the else result (no delay).
  • The multiplication by 555 is just to keep the expression numeric/to ensure type behavior in the injected context.
• Overall effect: If the condition is true, the database sleeps for 15 seconds, causing a noticeable delay in the response. If false, the query continues normally.

Why this is useful in exams

• It demonstrates the concept of time-based blind SQL injection: you don’t need visible error messages; you infer data by measuring how long the server takes to respond.
• It shows how attackers try to bypass input handling (closing quotes, using operators like XOR) to append their own logic to an existing query.
• It highlights why time-based methods are used: they work even when error messages are suppressed.

Common defenses (relevant for exam scenarios)

• Use parameterized queries / prepared statements everywhere. Do not concatenate user input into SQL.
• Validate and sanitize input with a strict whitelist; restrict allowed characters.
• Apply least privilege on the database account used by the application.
• Use stored procedures carefully and avoid dynamic SQL where possible.
• Web application firewall (WAF) with rule sets that detect typical SQL injection patterns.
• Enable proper error handling and avoid exposing database errors to users.
• For testing in labs, use a controlled environment (your own DB) and ensure you have authorization.

If you want, I can:

• Break down similar examples and show how a tester would infer a character of data using time delays.
• Provide a small, safe lab exercise that demonstrates time-based blind SQL injection in a controlled MySQL setup.