-1" OR 5*5=26 --

That looks like an SQL injection payload. Conceptually, it tries to manipulate a SQL query by:

• Closing an existing string literal (the -1" part).
• Injecting a tautology-like condition (OR 5*5=26) to alter the WHERE clause.
• Using -- to comment out the rest of the query so the original logic is bypassed.

What it would do (in typical SQL contexts):

• 5*5=26 is false (25 = 26 is not true).
• -1 is often treated as true in boolean contexts because it’s a nonzero number in many databases.
• If the injected fragment is evaluated as part of a WHERE clause, true OR false evaluates to true, which can bypass the intended checks.

Important safety note:

• I can’t help with exploiting systems. However, understanding why such payloads are dangerous and how to defend against them is great for exam prep.

Defenses you should know (high level):

• Use parameterized queries / prepared statements (never concatenate user input into SQL).
  • Examples:
    • In Python (psycopg2 or sqlite3): cursor.execute("SELECT * FROM users WHERE username = ?", (username,))
    • In Java (PreparedStatement): stmt = conn.prepareStatement("SELECT * FROM users WHERE username = ?");
• Avoid dynamic SQL. If you must build SQL, use safe APIs that bind values rather than string-concatenation.
• Validate and sanitize inputs, but don’t rely on escaping alone.
• Restrict database permissions (least privilege) so even if injection occurs, the attacker has limited access.
• Use a Web Application Firewall (WAF) and DB-level protections (disable multiple statements where possible, enable safe defaults).
• Consider using ORM layers that default to parameterized queries.
• Use input whitelisting for fields that have expected formats (e.g., emails, IDs).

If you want, tell me which DB and programming language you’re studying, and I’ll tailor a few safe, exam-focused examples (how to write parameterized queries, how to recognize injection risk in a given query, and some practice questions).