Question

555*if(now()=sysdate(),sleep(15),0)

Answer 1

What you posted is a common MySQL time-based SQL injection payload pattern:

555*if(now()=sysdate(),sleep(15),0)

What it does (high level)
- IF(condition, true_val, false_val) is a MySQL conditional expression.
- If the condition now() = sysdate() is true, the expression will call SLEEP(15), which pauses the database session for ~15 seconds; otherwise it evaluates to 0.
- Multiplying by 555 forces numeric evaluation; the real purpose is the delay, not the numeric result.
- SLEEP causes a noticeable response-time difference, so attackers can infer boolean conditions from timing. This is a typical time-based blind SQL injection probe.

Notes about NOW() vs SYSDATE()
- NOW() (CURRENT_TIMESTAMP()) returns the statement-start timestamp (constant for the statement).
- SYSDATE() returns the time at the moment of function execution.
- They may or may not be equal depending on timing and server behavior, so this condition is not guaranteed to be true—attackers often craft many variants to find one that triggers.

If you found this in logs or input
- Treat it as suspicious—likely an automated SQLi probe. Investigate the incoming request, source IP, user-agent and whether it reached the database or caused delays.

How to defend (recommended)
- Use parameterized queries / prepared statements for all DB access (never concatenate user input into SQL).
- Use input validation and allow-lists for expected values.
- Run your application with least-privilege DB accounts (no SUPER or unnecessary rights).
- Enable query logging / alerts for long-running queries and unusual SLEEP calls.
- Apply a Web Application Firewall (WAF) or intrusion prevention that can block common SQLi patterns.
- Set resource/time limits on queries where possible (e.g., proxy limits, max_execution_time).
- Keep database and application stacks patched and review code for dynamic SQL usage.

If you want help
- I can review a code snippet (server-side DB access code) and show how to convert it to parameterized queries or suggest logging rules and detection signatures. If you are testing for vulnerabilities, ensure you have authorization; I won’t provide step‑by‑step exploitation instructions.