Essential Web Application Security Checklist for Developers and Testers

Web applications are complex systems constantly exposed to potential threats. Ensuring their security requires a systematic approach throughout the development lifecycle and beyond. This checklist provides essential points for developers, testers, and security professionals to verify the security posture of a web application.

Use this checklist as a guide during development, testing phases (like QA and UAT), and periodic security reviews. It covers common vulnerability areas based on industry best practices and resources like the OWASP Top 10.

Web Application Security Checklist

1. Input Validation and Output Encoding

• [ ] Server-Side Validation: Is all user-supplied input (forms, URL parameters, HTTP headers, cookies, API inputs) rigorously validated on the server-side?
• [ ] Use Allow-Lists: Are inputs validated against strict allow-lists (permitted characters/formats) rather than block-lists?
• [ ] Type, Format, Length Checks: Are appropriate checks performed for data types, formats (e.g., email, date), and lengths?
• [ ] Contextual Output Encoding: Is data properly encoded before being rendered in HTML, JavaScript, CSS, or other contexts to prevent XSS?
• [ ] Parameterized Queries/Prepared Statements: Are parameterized queries or equivalent mechanisms used for all database interactions to prevent SQL Injection?
• [ ] File Upload Validation: Are file uploads restricted by type, size, and filename? Are uploaded files scanned for malware and stored securely outside the webroot?

2. Authentication

• [ ] Strong Password Policies: Are complexity, length, and history requirements enforced?
• [ ] Secure Password Storage: Are passwords hashed using strong, salted, adaptive algorithms (e.g., bcrypt, Argon2)?
• [ ] Multi-Factor Authentication (MFA): Is MFA implemented for sensitive accounts and actions?
• [ ] Account Lockout Mechanism: Is there protection against brute-force login attempts (e.g., temporary lockout, CAPTCHA)?
• [ ] Secure Password Reset: Is the password reset process secure (e.g., using time-limited, unpredictable tokens sent via a secure channel)?
• [ ] Protection Against Credential Stuffing: Are measures in place to detect or prevent automated credential stuffing attacks?

3. Session Management

• [ ] Strong Session Identifiers: Are session IDs long, random, and unpredictable?
• [ ] Secure Transmission: Are session IDs transmitted only over HTTPS?
• [ ] Cookie Security Flags: Are HttpOnly and Secure flags set for session cookies? Is the SameSite attribute used appropriately (Lax or Strict)?
• [ ] Session Timeouts: Are reasonable inactivity and absolute session timeouts enforced?
• [ ] Session ID Regeneration: Is the session ID regenerated upon login, logout, and privilege level changes?
• [ ] Secure Logout: Does the logout function properly invalidate the session on the server-side?

4. Authorization / Access Control

• [ ] Principle of Least Privilege: Do users have only the minimum necessary permissions?
• [ ] Role-Based Access Control (RBAC): Is access control managed based on well-defined roles?
• [ ] Enforcement on Server-Side: Is access control enforced on the server for every request, not just relying on hiding UI elements?
• [ ] Test for Horizontal Privilege Escalation (IDOR): Can a user access resources belonging to another user at the same privilege level by manipulating identifiers?
• [ ] Test for Vertical Privilege Escalation: Can a lower-privileged user access functions or data intended for higher-privileged users (e.g., administrators)?
• [ ] Secure Direct Object References: Are internal object references mapped to indirect references shown to the user, or are access checks performed on every request using direct references?

5. Cryptography & Data Protection

• [ ] HTTPS Everywhere: Is TLS/SSL enforced for all application traffic?
• [ ] Strong TLS Configuration: Are up-to-date protocols (TLS 1.2+) and strong cipher suites used? Are weak protocols/ciphers disabled?
• [ ] HSTS Header: Is the Strict-Transport-Security header implemented?
• [ ] Sensitive Data Encryption at Rest: Is sensitive data (e.g., PII, financial information) encrypted when stored in databases or files?
• [ ] Appropriate Algorithm Use: Are standard, vetted cryptographic algorithms and libraries used correctly? Avoid custom cryptography.

6. Security Configuration

• [ ] Secure Server Configuration: Is the web server, application server, and database securely configured (e.g., disabling unnecessary services/modules, secure defaults)?
• [ ] Security Headers: Are appropriate security headers implemented (Content-Security-Policy, X-Content-Type-Options, X-Frame-Options, Referrer-Policy)?
• [ ] Error Handling: Are generic, non-revealing error messages shown to users? Are detailed errors logged securely on the server?
• [ ] Dependency Management: Are third-party libraries and components kept up-to-date and checked for known vulnerabilities (SCA)?
• [ ] Unnecessary Features Disabled: Are default accounts, unused features, and debug modes disabled in production?

7. Logging and Monitoring

• [ ] Sufficient Logging: Are security-relevant events (logins, logouts, access control failures, significant errors, key transactions) logged?
• [ ] Log Protection: Are logs protected from unauthorized access and tampering?
• [ ] No Sensitive Data in Logs: Are passwords, session IDs, API keys, or other sensitive data excluded from logs?
• [ ] Monitoring & Alerting: Are systems in place to monitor logs for suspicious activity and generate alerts?

Conclusion

This checklist provides a starting point for assessing web application security. It should be adapted based on the specific application's technology stack, business logic, and risk profile. Regularly reviewing and testing against these points, ideally integrating them into automated checks and manual reviews, is crucial for building and maintaining secure web applications. Remember that security is a continuous process, not a one-time task.