-1' OR 5*5=26 --

This looks like an SQL injection payload.

What it does (in brief):

• -1' ends a quoted string in a SQL query.
• OR 5*5=26 injects a boolean condition (here 25=26 is false).
• The trailing -- comments out the rest of the statement.

In other words, if a program naively builds a SQL query by concatenating user input, this input could alter the logic of the query. A typical risky goal is to bypass checks or reveal data; a true-vs-false injection often uses something like OR 1=1 to always be true.

Key defensive points:

• Use parameterized queries or prepared statements everywhere. Do not interpolate user input directly into SQL.
• Validate and sanitize input with allowlists; enforce appropriate data types and lengths.
• Apply least-privilege access for the database user (e.g., no read/write permissions when not needed).
• Consider using ORM/abstraction layers and stored procedures with parameters.
• Consider runtime protections like WAF rules and proper error handling to avoid leaking details.

quick examples:

• Vulnerable (conceptual): query = "SELECT * FROM users WHERE username = '" + userInput + "'" If userInput = "-1' OR 5*5=26 --", the final query could become: SELECT * FROM users WHERE username = '-1' OR 25=26 --'

• Secure (parameterized): In many languages:

  • Python (sqlite3/psycopg2): cursor.execute("SELECT * FROM users WHERE username = ?", (userInput,))
  • Java (JDBC): PreparedStatement ps = conn.prepareStatement("SELECT * FROM users WHERE username = ?"); ps.setString(1, userInput);

If you’re studying this for an exam, I can tailor explanations to your syllabus (e.g., highlighting how and why injections succeed, common payloads, or defensive design patterns). Do you want a worked example in a specific language or a focus on defense?