555-1)) OR 875=(SELECT 875 FROM PG_SLEEP(15))--

That string looks like a time-based blind SQL injection payload for PostgreSQL, using the pg_sleep function.

What it does (high level):

• The attacker tries to append or inject SQL into an existing query so that the database executes an extra condition.
• If the condition is met, the database is told to sleep (delay) for a set amount of time (e.g., 15 seconds).
• By measuring how long the application takes to respond, the attacker can infer information about the database (even without seeing query results).

Important: I can’t help with exploiting systems. If you’re studying this for an exam, I can help with safe, defensive explanations and lab-oriented practice.

Defensive measures (high level):

• Use parameterized queries / prepared statements for all user input. Do not concatenate user input into SQL strings.
• Validate and sanitize input with strict typing and whitelisting (e.g., integers where integers are expected).
• Apply the principle of least privilege: run the application’s database user with only the necessary rights; avoid accounts with superuser privileges.
• Disable or restrict dangerous functions if possible (e.g., restrict usage of pg_sleep or similar functions to trusted roles).
• Enable per-query timeouts at the database or application layer (e.g., statement_timeout in PostgreSQL).
• Use a web application firewall (WAF) and intrusion detection to flag unusual patterns like time delays or suspicious concatenations.
• Regularly scan for SQL injection vulnerabilities in test environments and keep PostgreSQL and dependencies up to date.
• Log and monitor long-running queries and anomaly response times for early detection.

If you want, I can:

• Create a short, exam-focused summary of SQL injection concepts.
• Provide safe practice questions or lab scenarios that illustrate detection and prevention (without actionable exploitation steps).