Clarify first

• Is the form authenticated or public-facing?
• What data does it collect, and is user-generated content rendered back to other users?
• What is the tech stack (helps scope injection surface — Rails, Django, Spring, Node)?
• Are there any known compliance requirements (PCI, HIPAA, GDPR) that constrain data handling?

Injection & content security

• XSS — inject <script>alert(1)</script> and <img src=x onerror=alert(1)> in every text field; verify stored output is HTML-encoded and no script executes
• SQL injection — inject ' OR '1'='1 and '; DROP TABLE users; -- in every field; no DB error surfaced, no data returned
• HTML injection — inject <h1>Owned</h1> to verify the response is not raw HTML
• Command injection — inject ; ls -la if any field is used in a server-side shell command

Transport security

• Form submits over HTTPS; any HTTP attempt is redirected to HTTPS
• Sensitive fields (password, card, SSN) not in the URL query string
• autocomplete="off" on password and card fields

Authentication & authorisation

• CSRF: token present in the form; removed or tampered token causes the submission to be rejected
• Unauthenticated submission to an authenticated endpoint returns 401/403 (not silently accepted)
• IDOR: form submission referencing another user's resource ID is rejected

Data handling

• PII collected by the form is not logged in plaintext server-side (check application and access logs)
• Sensitive values not echoed in error messages or HTTP response headers
• Server-side validation enforced independently of client-side validation (disable JS and re-submit)

Rate limiting & abuse

• Brute-force protection on login/registration forms (lockout or CAPTCHA after repeated submissions)
• Submission rate limit applied per user or IP

Close: automate injection payloads using OWASP ZAP or Burp Suite in CI-integrated scan mode, plus targeted unit tests for each validator. Keep manual for logic-level abuse scenarios and reviewing server logs for data leakage.