That looks like an SQL‑injection payload meant to trigger a time delay in a PostgreSQL database (a time‑based blind SQLi test). Brief breakdown:
- The initial apostrophe (' / ') is used to break out of a string literal in the original query.
- The OR ... expression tries to inject a boolean condition.
- 742=(SELECT 742 FROM PG_SLEEP(15)) is intended to make the database execute pg_sleep(15) (sleep for 15 seconds) and then evaluate the condition.
- The -- comments out the rest of the original SQL so the injected part executes alone.
- A delayed response indicates the injected expression was evaluated, which is a common way to detect blind SQL injection vulnerabilities.
Important: do not run injection tests against systems you do not own or have explicit permission to test.
How to mitigate and detect this class of attack
- Use parameterized queries / prepared statements (bind parameters) everywhere — never concatenate user input into SQL.
- Apply strict input validation / whitelisting for expected values wherever possible.
- Use ORM query APIs that avoid raw SQL, or safely parameterize any raw SQL.
- Run the DB with least privilege for the application account (no superuser privileges).
- Restrict or revoke EXECUTE on dangerous functions where feasible (e.g., pg_sleep) for non‑trusted roles.
- Deploy a WAF / Web Application Firewall and add rules to flag patterns like pg_sleep, sleep(, waitfor delay, long response times, or suspicious comment markers.
- Monitor logs and alert on unusual latency spikes for input that looks like injection attempts.
- Rate‑limit unauthenticated endpoints and require authentication where appropriate.
- Do regular authorized security testing (code review, static analysis, and penetration testing).
If you want, tell me what language/framework and a short code snippet (the vulnerable query), and I can show a secure, parameterized version and specific hardening suggestions.