-1' OR 5*5=26 or 'GH5LGdEn'='

What you posted looks like an SQL injection payload fragment. It seems to be trying to break out of a quoted string and inject an OR condition into a SQL statement.

Key idea:

• -1' attempts to terminate a string literal in the SQL query.
• OR 55=26 adds a boolean expression to alter the WHERE clause. Since 55=26 is false (25 would be true), this particular piece would not be a tautology. The rest ('GH5LGdEn'=' ) also looks like an attempt to manipulate string comparisons.
• In a vulnerable query, this could change which rows get returned (and in some cases could lead to errors or disclosure of information).

Why this matters:

• If user input is concatenated directly into SQL (no parameterization), attackers can alter the query logic and potentially bypass authentication or access data they shouldn’t.

Defensive takeaways (exam-ready):

• Never build SQL by concatenating user input. Use prepared statements/parameterized queries.
• Validate and normalize inputs (e.g., enforce types, lengths, allowlists).
• Use least-privilege database accounts; don’t expose admin rights through the app.
• Use an ORM or a query builder that handles parameter binding.
• Suppress detailed database error messages to users; log them server-side.
• Consider input sanitization as a defense-in-depth layer, but don’t rely on it alone.

Quick example:

• Vulnerable: SELECT * FROM users WHERE username = 'user_input';
• Secure: SELECT * FROM users WHERE username = ?; (and pass user_input as a parameter)

If you want, I can tailor explanations or a tiny practice exercise to your course (e.g., show how a vulnerable snippet is fixed with parameterized queries in a specific language).