-1' OR 5*5=25 --

That looks like a classic SQL injection payload.

What it does (high level):

• The -1' tries to terminate a string literal in a SQL query.
• OR 5*5=25 adds a condition that is always true (since 25 = 25), so the WHERE clause becomes effectively true.
• -- starts a SQL comment, so the rest of the original query is ignored.

Example context (vulnerable code):

• Suppose a login query like: SELECT * FROM users WHERE username = '$input' AND password = '$password';
• If $input = -1' OR 55=25 --, the query becomes: SELECT * FROM users WHERE username = '-1' OR 55=25 --' AND password = '$password'; The OR true condition makes the WHERE clause true, potentially bypassing authentication or returning unintended data.

How to defend (quick guidance):

• Use parameterized (prepared) statements for all SQL queries. Do not interpolate user input directly.
  • Example (language-agnostic):
    • SELECT * FROM users WHERE username = ? AND password = ?
    • Bind user-provided values as parameters, not as part of the string.
• Validate and constrain inputs (type, length, allowed characters) and implement allowlists.
• Use ORM/query builders that automatically parameterize queries.
• Apply the principle of least privilege to the database user (e.g., read/write restrictions as appropriate).
• Disable detailed error messages that reveal SQL syntax or structure.
• Consider additional defenses like WAFs or input sanitization, but do not rely on escaping alone.

If you want, I can show concrete code snippets in your preferred language to demonstrate safe querying and how this payload would be neutralized.