Web application security is still often treated as something to address “later.” In practice, however, most security incidents are not caused by sophisticated attacks, but by basic design and implementation mistakes.
In this article, we cover the most common security mistakes that regularly appear in web applications — regardless of project size.
Lack of Input Validation
One of the most common problems is trusting user-provided data. Every form field, URL parameter, or JSON payload can be manipulated.
Missing input validation can lead to:
- SQL Injection,
- Command Injection,
- uncontrolled application errors.
Validation should always be performed on the backend, regardless of frontend validation.
Improper Session and Authorization Management
Session handling issues are a frequent cause of account takeovers. Typical problems include:
- overly long session lifetimes,
- lack of token invalidation,
- missing session ID rotation after login.
Authorization must always be enforced on the server side and should never rely on client-provided data.
Missing Protection Against XSS and CSRF
Cross-Site Scripting (XSS)
XSS allows attackers to execute arbitrary JavaScript in the context of an application. It most often results from:
- missing data sanitization,
- rendering user input without proper escaping.
Cross-Site Request Forgery (CSRF)
CSRF enables actions to be performed on behalf of an authenticated user without their knowledge. Effective protection includes:
- CSRF tokens,
- appropriate SameSite cookie headers.
Storing Sensitive Data in Plain Text
Passwords, API tokens, and private keys should never:
- be stored in source code,
- be committed to repositories,
- be stored in plain text.
Passwords must be hashed using algorithms such as bcrypt or argon2.
Outdated Dependencies
Outdated libraries are one of the easiest attack vectors. Regular updates and automated dependency scanning (e.g., Dependabot) should be standard practice.
Summary
Web application security starts with fundamentals. Consciously avoiding common mistakes significantly reduces the risk of attacks and costly production incidents.