5550"XOR(555*if(now()=sysdate(),sleep(19.946),0))XOR"Z

Short answer: that looks like a time-based blind SQL injection payload, intended to test or exploit a MySQL-like database by using a conditional Sleep to create a detectable delay.

What the pieces do (high level):

• if(now()=sysdate(), sleep(19.946), 0)
  • now() and sysdate() are time functions. In some MySQL setups they can be equal only for a short window (e.g., when both are measured in the same second without fractional parts), so the condition may be true only very occasionally.
  • If the condition is true, the SLEEP(19.946) call pauses the query for about 19.9 seconds; otherwise it returns 0 immediately.
• The surrounding 555*... and the leading 5550 / trailing XOR"Z" are typically there to:
  • try to fit the payload into a particular query context or to bypass naive input filters,
  • or to produce a specific numeric/string result after the evaluation (the exact syntax here isn’t standard SQL, but the intent is to combine the sleep delay with a numeric XOR expression).
• In practice, the attacker observes the response time:
  • if the response is delayed by about 20 seconds, the condition was true (vulnerability exists and the time-based condition can be exploited);
  • if there’s no delay, the condition was false (no vulnerability or not in that exact timing window).

Important caveats:

• This is a defensive explanation, not a how-to. Using or testing such payloads on systems you don’t own or don’t have explicit permission to test is illegal and unethical.
• Time-based blind injections rely on timing side channels, and modern applications often employ mitigations that reduce the reliability of such tests.

Defensive measures (to prevent this kind of vulnerability):

• Use parameterized queries / prepared statements. Do not interpolate user input into SQL strings.
• Apply strong input validation and white-listing where appropriate.
• Least privilege: run the application with a DB user that has only the needed permissions.
• Disable or tightly control functions that cause side effects (e.g., SLEEP) if not needed by the app.
• Use a web application firewall (WAF) and consider query-logging/monitoring to detect unusual patterns.
• Regularly test in a legal, controlled environment (e.g., your own lab or a sanctioned security assessment) using safe, approved tools and methodologies.

If you’re studying for an exam, I can help you with:

• a clean theoretical explanation of time-based blind SQL injection and why NOW() = SYSDATE() is used,
• how to recognize such payloads in logs,
• and how to defend against them, plus some safe practice questions or lab setup guidance (in an ethics-approved environment).