-1' OR 5*5=26 --

This looks like a classic SQL injection payload.

What it does (high level):

• It tries to terminate a string literal in a SQL query, then injects an OR condition, and finally uses a comment to ignore the rest of the query.
• For a vulnerable query like: SELECT * FROM users WHERE username = '$input';
  • If input is -1' OR 55=26 --, the query becomes: SELECT * FROM users WHERE username = '-1' OR 55=26 --';
  • The -- comments out the trailing quote, so the WHERE clause effectively becomes: username = '-1' OR 5*5=26.
  • Since 5*5=26 is false, the condition reduces to username = '-1' unless a row with that username exists.

Key points:

• 5*5=26 is false (25 equals 26 is not true). Attaching OR with a false expression doesn’t automatically grant access.
• The typical attack aims for OR 1=1 or similar to always be true, e.g., ' OR 1=1 -- which would bypass checks if the DB engine and query structure allow it.

For exam context:

• Understand the mechanism: end the string, inject OR condition, and comment out the rest.
• Know which part makes the payload work: the quote, the OR, and the comment (--) to neutralize trailing syntax.

Defensive practices (essential for exams and real life):

• Use parameterized queries / prepared statements so user input is never concatenated into SQL.
• Example (Python with sqlite3):
  • cur.execute("SELECT * FROM users WHERE username = ?", (username,))
• Example (PHP PDO):
  • $stmt = $pdo->prepare("SELECT * FROM users WHERE username = :user");
  • $stmt->execute(['user' => $username]);
• Validate and sanitize inputs, apply least privilege on the database user, and consider using ORM features that parameterize queries automatically.

If you want, I can tailor a quick mock example in the language you’re studying (Python, Java, PHP, etc.) to illustrate both the vulnerable vs. safe approach.