-1' OR 5*5=26 --

This looks like a SQL injection payload. It’s designed to tamper with a query by injecting extra SQL logic through user input.

What each part does (in a typical vulnerable query)

• -1' ends a string literal. For example, if the code builds a SQL like: ... WHERE user = '$input', the -1' would close the quoted value.
• OR introduces an alternate boolean condition.
• 5*5=26 is a boolean expression (false, since 25 ≠ 26). Its value would participate in the OR.
• -- starts a comment, so the rest of the line is ignored by the SQL parser. This can hide the remainder of the original query.

Effect depends on the surrounding query:

• In a naive vulnerable query like: SELECT * FROM users WHERE username = '$input' AND password = '$pass'; If input is -1' OR 55=26 --, the query becomes something like: SELECT * FROM users WHERE username = '-1' OR 55=26 The 5*5=26 part is false, so it’s basically username = '-1' OR false, which is unlikely to match anything. If the attacker used a tautology like ' OR 1=1 --, the condition would be always true and could bypass checks.
• In practice, the key idea is to demonstrate how unsafely concatenated input can alter the logic of a query.

Common exam takeaways

• The danger comes from placing untrusted input directly into SQL strings.
• A tautology (for example, 1=1) or an always-true condition is what attackers try to inject to bypass authentication.
• The exact outcome with 5*5=26 depends on the surrounding query; with a true condition, it can bypass; with a false condition, it might not.

Defensive measures (how to stop this)

• Use parameterized queries / prepared statements (bind user input as parameters, not as SQL code).
  • Example (conceptual): SELECT * FROM users WHERE username = ? AND password = ?
  • Language examples:
    • Python: cursor.execute("SELECT * FROM users WHERE username = %s AND password = %s", (username, password))
    • Java: PreparedStatement ps = conn.prepareStatement("SELECT * FROM users WHERE username = ? AND password = ?"); ps.setString(1, username); ps.setString(2, password);
• Avoid dynamic SQL built by string concatenation.
• Validate and sanitize inputs, but don’t rely on sanitization alone.
• Apply least-privilege database accounts and proper error handling.
• Consider a web application firewall and disable unsafe features (like exposed debug errors).

If you want, tell me your target language or the exam style, and I can tailor a quick example (unsafe vs. safe) to illustrate these concepts.