Input Validation

In web application security, user input and its associated data are a security risk if left unchecked. We address these problems by using "Input Validation" and "Input Sanitization" techniques. These validations should be performed in every tier of the application, as per the server's function. An important note is that all data validation procedures must be done on trusted systems (i.e. on the server).

As noted in the OWASP SCP Quick Reference Guide, there are sixteen bullet points that cover the issues that the developer should be aware of when dealing with Input Validation. A lack of consideration for these security risks when developing an application is one of the main reasons Injection ranks as the number 1 vulnerability in the "OWASP Top 10".

User interaction is a staple of the current development paradigm in web applications. As web applications become increasingly richer in content and possibilities, user interaction and submitted user data also increases. It is in this context that Input Validation plays a significant role.

When applications handle user data, submitted data must be considered insecure by default, and only accepted after the appropriate security checks have been made. Data sources must also be identified as trusted, or untrusted, and in case of an untrusted source, validation checks must be made.

In this section an overview of each technique is provided, along with a sample in Go to illustrate the issues.

• Validation
  1. User Interactivity
     • Whitelisting
     • Boundary checking
     • Character escaping
     • Numeric validation
  2. File Manipulation
  3. Data sources
     • Cross-system consistency checks
     • Hash totals
     • Referential integrity
     • Uniqueness check
     • Table look up check
• Post-validation Actions
  1. Enforcement Actions
     • Advisory Action
     • Verification Action
• Sanitization
  1. Check for invalid UTF-8
     • Convert single less-than characters (<) to entity
     • Strip all tags
     • Remove line breaks, tabs and extra white space
     • Strip octets
     • URL request path