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Networking basics, Handling User Input Safely

Every time your application accepts data from a user, it opens the door to potential vulnerabilities. Improper handling of user input is one of the top causes of security breaches. This guide covers how to safely handle input to protect your application and users.

Step 1: Validate Input

Always check that user input matches expected formats and values:

  • Use whitelisting (accept only expected characters/values).
  • Reject or sanitize unexpected input.
  • Use input constraints (e.g., max length, regex patterns).

Step 2: Sanitize Input

Remove or escape characters that could be used maliciously:

  • Escape HTML to prevent XSS.
  • Escape SQL to prevent injection.

Example (in C-style pseudocode):

char* clean = escape_html(user_input);

Step 3: Use Parameterized Queries

Never build SQL queries by concatenating strings with input:

-- BAD
    query = "SELECT * FROM users WHERE name = '" + name + "'";

    -- GOOD
    query = db.prepare("SELECT * FROM users WHERE name = ?");
    query.bind(name);

Step 4: Limit Input Size and Type

Restrict length and character sets to prevent buffer overflows and excessive data uploads.

Step 5: Avoid Trusting Client-Side Validation

Client-side checks (like JavaScript form validation) can be bypassed. Always validate and sanitize input on the server.

Step 6: Use Libraries and Frameworks

Use established frameworks with built-in protection and input handling mechanisms.

Next Steps

Audit your forms and input points. Ensure proper validation and sanitization is in place. Consider using security linters or static analysis tools to catch unsafe patterns early.