BLOG
Top 10 Input Fields Vulnerable to OWASP Top 10:
(And How to Test Them)
- April 20, 2026
Every web application relies heavily on user input fields to drive interactivity, collect data, and deliver a seamless user experience. However, these seemingly innocent text boxes, dropdowns, and file upload zones frequently double as open invitations for malicious cyberattacks. To build secure software, QA engineers and automation specialists must adopt an adversarial mindset, treating every entry point as a potential security breach. In this comprehensive technical guide, we will break down the top 10 input fields vulnerable to OWASP Top 10 flaws, providing actionable manual and automation testing techniques to ensure your web applications remain robust against sophisticated exploitation.
1. The Search Bar
Primary Vulnerability: A03:2021-Injection (SQLi, NoSQLi)
The Threat: The quintessential text input. Developers routinely construct dynamic database queries using whatever the user types here. If they fail to parameterise inputs, chaos ensues.
How to Test: Inject classic SQL syntax such as ‘ OR ‘1’=’1 or a script tag like <script>alert(1)</script>. If the page returns a database syntax error or triggers an unintended pop-up, you have successfully exposed a critical security flaw.
2. The Login Form (Username/Password)
Primary Vulnerability: A07:2021-Identification and Authentication Failures
The Threat: Login inputs are prime targets for automated credential stuffing and brute-force attacks. They are also notoriously susceptible to SQL Injection designed to bypass authentication entirely.
How to Test: Attempt to log in with admin’ — as the username. Fire up an automation tool like Playwright to simulate 50 rapid login requests from a single IP. If the system fails to lock the account or enforce a CAPTCHA, your authentication controls are lacking.
Advertisement
3. The 'Profile Picture' File Upload Zone
Primary Vulnerability: A01:2021-Broken Access Control
The Threat: File uploaders are incredibly dangerous. If an application blindly trusts a user-supplied file, an attacker might upload a reverse shell script rather than a charming JPEG.
How to Test: Rename a basic PHP web shell script to malicious.jpg.php or change its MIME type in transit. Upload it, then try to access its URL directly. If the server executes the script, the application’s file validation mechanisms are fundamentally broken.
4. The Comment Section / Rich Text Editor
Primary Vulnerability: A03:2021-Injection (Stored Cross-Site Scripting – XSS)
The Threat: Any field designed to store text and display it to other users is vulnerable to Stored XSS. If your app saves malicious scripts to the database, every subsequent visitor will execute them.
How to Test: Submit HTML and JavaScript payloads disguised as text, such as <img src=x onerror=alert(document.cookie)>. Reload the page using a different session to check if the script executes and attempts to harvest your session data.
5. Hidden Form Fields (e.g., Price or Item ID)
Primary Vulnerability: A01:2021-Broken Access Control
The Threat: Developers sometimes fall into the trap of hiding variables inside <input type=”hidden”> elements, naively assuming users cannot alter them. Attackers love proving them wrong.
How to Test: Open your browser’s Developer Tools, inspect the DOM, and locate the hidden price field. Change the value from £99.99 to £0.01 and submit the form. If the checkout accepts the modified price, the system lacks server-side verification.
6. The URL Parameter / ID Field
Primary Vulnerability: A01:2021-Broken Access Control (Insecure Direct Object References – IDOR)
The Threat: Though strictly part of the query string, parameters like ?account_id=1004 function exactly like input fields. Manipulating these values tests for IDOR.
How to Test: Log in as User A and note your account ID. Manually alter the URL parameter to match User B’s ID (e.g., changing 1004 to 1005). If you can view or modify User B’s private account dashboard, horizontal privilege escalation is present.
7. The Voucher / Promo Code Box
Primary Vulnerability: A04:2021-Insecure Design / Business Logic Flaws
The Threat: Promo code inputs frequently lack strict business logic validation, opening the door for concurrency flaws, mathematical exploitation, or unexpected type errors.
How to Test: Apply a promo code twice simultaneously using an automated API script to see if the discount duplicates. Alternatively, enter negative numbers or boundary value limits to observe how the total calculation behaves mathematically ().
8. The 'Forgot Password' Email Field
Primary Vulnerability: A05:2021-Security Misconfiguration
The Threat: This field often leaks vital data. Verbose error messages can accidentally map out your user base, facilitating targeted phishing campaigns.
How to Test: Type an email address that definitely does not exist. If the application returns “Email address not found”, it allows user enumeration. A secure system should always reply neutrally: “If that account exists, an email has been sent.”
9. The Currency / Quantity Dropdown
Primary Vulnerability: A03:2021-Injection & Validation Bypass
The Threat: Because a dropdown restricts user choices in the UI, developers often skip server-side validation. However, intercepting and changing the transmitted value is trivial.
How to Test: Use a proxy tool like OWASP ZAP to intercept the POST request when submitting the form. Modify the selected option from a legitimate currency code to an exploitation payload or an invalid string, then forward the request to check server stability.
10. The Webhook / Integration URL Input
Primary Vulnerability: A10:2021-Server-Side Request Forgery (SSRF)
The Threat: Fields that accept external URLs (such as webhooks or profile link scrapers) can be manipulated to trigger SSRF, forcing your server to attack internal resources.
How to Test: Instead of providing a public URL, input local loopback addresses such as http://127.0.0.1:8080 or http://169.254.169.254 (cloud metadata services). If the server leaks internal system information, it is dangerously vulnerable.
The Golden Rule of Input Security
Securing web applications requires adhering to a fundamental engineering principle: never trust client-side data. Frontend validation is an excellent tool for guiding users and improving the user experience, but it provides zero actual security. Every single input field must be rigorously validated, sanitised, and parameterised on the server side. As professional software testers, it is our responsibility to break things intentionally in staging so they never break catastrophically in production. Happy testing!