web-application-security

Web Application Security

Vulnerability Classes

Category	Threats
Input validation	Command injection, SQL injection, Cross-Site Scripting (XSS)
Upload handling	Local File Inclusion (LFI), Remote File Inclusion (RFI)
Session management	Man-in-the-Middle (MITM), session fixation, session hijacking
Data exposure	Cleartext data theft, insecure storage, cache leaks
Authentication	Credential stuffing, brute force, account enumeration
Access control	Privilege escalation, IDOR, missing function-level checks

Security Requirements

Server-Side Controls

All security controls MUST be implemented server-side. Client-side validation is a UX convenience, not a security boundary. This applies to:

• Input validation and sanitization
• Upload type and size restrictions
• Authentication and session management
• Authorization decisions

Network-Level Protections

• Deploy a Web Application Firewall (WAF) in front of public-facing applications where feasible
• Enable DDoS protection on Internet-facing endpoints
• Terminate TLS at the edge; enforce HTTPS end-to-end

CORS

• Configure Cross-Origin Resource Sharing to allow only known, explicitly listed origins
• Never use wildcard (*) origins on endpoints that accept credentials
• Validate the Origin header server-side before reflecting it

CSRF Protection

• Enable framework-provided CSRF token mechanisms (e.g., Django CSRF middleware, Spring CSRF, Rails protect_from_forgery)
• Use SameSite cookie attributes as a defense-in-depth layer
• Verify tokens on every state-changing request

Session Management

• Generate a new session ID after successful authentication (prevent session fixation)
• Never expose session IDs in URLs
• Store session tokens in secure, HttpOnly, SameSite cookies
• Invalidate sessions on logout, idle timeout, and absolute timeout
• Bind sessions to client fingerprint where feasible (IP, User-Agent)

Sensitive Data Handling

• Encrypt sensitive data in transit (TLS 1.2+) and at rest
• Do not store sensitive data longer than necessary
• Disable caching for responses containing sensitive data (Cache-Control: no-store)
• Never log passwords, tokens, or PII

Authentication Hardening

• Implement multi-factor authentication for privileged or Internet-facing accounts
• Use uniform error responses for login, registration, and credential recovery to prevent account enumeration (e.g., "Invalid credentials" regardless of whether the username exists)
• Enforce account lockout or progressive delays after repeated authentication failures

Access Control

• Adopt least-privilege and deny-by-default for every request
• Route all requests through a centralized access-control verification layer
• Enforce authorization on direct object references; never rely on obscurity of IDs
• Re-validate privileges on long-lived sessions

Implementation Checklist

• All validation and authorization logic runs server-side
• WAF or equivalent network protection is in place for public endpoints
• CORS whitelist is explicit (no wildcard with credentials)
• CSRF tokens are validated on every state-changing request
• Session IDs rotate after authentication
• Sessions are invalidated on logout and timeout
• Sensitive data responses set Cache-Control: no-store
• MFA is available for Internet-facing authentication
• Login/registration/recovery responses are uniform (no enumeration)
• Every request passes through centralized access-control checks

References

• OWASP Input Validation Cheat Sheet
• OWASP CSRF Prevention Cheat Sheet
• OWASP Transport Layer Security Cheat Sheet
• OWASP Proactive Controls: Protect Data Everywhere
• OWASP Proactive Controls: Enforce Access Controls