Input Validation Testing

Overview

Input validation testing examines how web applications handle user-supplied data to identify vulnerabilities that occur when applications fail to properly validate, sanitize, or encode input before processing. These vulnerabilities represent some of the most critical security flaws in web applications, often leading to complete system compromise, data breach, or unauthorized access.

Why Input Validation Testing Matters

Critical Security Impact:

• Direct access to backend databases and systems

• Remote code execution on servers

• Complete application and server compromise

• Data exfiltration and unauthorized access

• Cross-site attacks against other users

Root Cause Analysis: Input validation vulnerabilities stem from developers trusting user input without proper verification, allowing malicious data to be processed as legitimate commands, queries, or code.

Testing Approach

Systematic Input Testing Methodology

Input Point Identification:

• Form fields and parameters

• HTTP headers and cookies

• File upload mechanisms

• API endpoints and JSON/XML data

• URL path components

Injection Testing Strategy:

• Identify injection points through error analysis

• Craft payloads specific to backend technologies

• Test for different injection contexts and encodings

• Validate successful exploitation through observable responses

Chapter Structure

This chapter covers the most critical input validation vulnerabilities:

Database Injection Attacks

1. SQL Injection (All Variants) - Traditional databases with Union, Boolean, Time-based, and Error-based techniques

2. NoSQL Injection - MongoDB, CouchDB, and other NoSQL database exploitation

Code Injection Vulnerabilities

1. Cross-Site Scripting (XSS) - Stored, Reflected, and DOM-based client-side code injection

2. Command Injection - Operating system command execution through application input

3. Template Injection (SSTI) - Server-side template engine exploitation

Data Format Injection

1. LDAP Injection - Directory service query manipulation

2. XML Injection (XXE) - XML External Entity attacks and XML processing vulnerabilities

File System Attacks

1. Path Traversal - Directory traversal and file system access

2. File Upload Vulnerabilities - Malicious file upload and processing attacks

Protocol-Level Attacks

1. HTTP Parameter Pollution - Parameter parsing inconsistencies

2. HTTP Request Smuggling - HTTP request processing manipulation

Modern Input Validation Challenges

API-First Applications:

• JSON and XML injection in REST APIs

• GraphQL injection attacks

• Microservices input validation boundaries

Cloud and Container Environments:

• Container escape through input validation

• Cloud service injection attacks

• Serverless function input processing vulnerabilities

This systematic approach ensures comprehensive coverage of input validation vulnerabilities while providing practical testing methodologies for each attack vector.