-1' OR 5*5=25 --

That’s a classic SQL injection payload.

• What it does: It tries to terminate a string literal in a SQL query (the -1' part), injects a condition that is always true (5*5=25), and then uses -- to comment out the rest of the query. If the query is vulnerable, the WHERE clause can become tautological, potentially bypassing authentication or exposing data.

• Why it works: If user input is directly concatenated into SQL, the attacker can alter the logic of the query rather than treating the input as data.

• How to defend (exam-ready tips):

  • Use parameterized queries / prepared statements instead of string concatenation.
  • Validate and type-check inputs (e.g., ensure IDs are integers when required).
  • Use ORM or binding mechanisms that safely escape inputs.
  • Minimum privilege for the DB user and avoid multi-statement execution.
  • Consider input length limits and allow-list patterns.
  • Employ a Web Application Firewall (WAF) as a secondary defense.

• Quick examples:

  • Vulnerable pattern (conceptual): SELECT * FROM users WHERE username = 'INPUT';
  • Attack string: -1' OR 5*5=25 -- (as you provided) could turn the query into something always true.
  • Safe pattern: SELECT * FROM users WHERE username = ? (bindings: [username]) or use: cursor.execute("SELECT ... WHERE username = %s", (username,))

If you want, I can tailor a short, language-specific example (Python, Java, Node.js) showing both the vulnerable pattern and a safe fixed version.