How to Identify Vulnerabilities in Web Applications: A Practitioner's Approach
Updated: 5 days ago
Web applications are where your business logic, customer data and transactions live. Automated scanners are good at finding some issues there, such as reflected cross-site scripting, missing security headers and outdated libraries. They are poor at the issues that cause the most damage: broken authorization, flawed authentication flows and business logic abuse. Finding those takes a methodical, manual approach.
Start from established references
The OWASP Top 10:2025 is a useful map of risk. Broken Access Control remains in first place, followed by Security Misconfiguration, while Software Supply Chain Failures, which expands the former Vulnerable and Outdated Components category, now ranks third. For detailed test cases, the OWASP Web Security Testing Guide (WSTG) is the practical companion, and the OWASP ASVS 5.0 defines verification requirements you can test against.
1. Map the application
Before testing anything, understand it. Identify every user role, every workflow and every API endpoint, including the backends used by single-page and mobile apps. Route all traffic through an intercepting proxy such as Burp Suite or OWASP ZAP, and read the JavaScript bundles: they often reveal API routes and parameters that the interface never shows.
2. Test access control
This is where the most serious findings usually are. For every endpoint, repeat requests with each role's session and with no session at all:
Insecure direct object references: change an invoice, order or user ID and see whether you get someone else's data.
Vertical privilege escalation: call administrative functions with a regular user's token.
Tenant isolation: in multi-tenant platforms, confirm that one customer can never read or modify another customer's records.
3. Test authentication and session management
Verify that MFA is enforced on every path, including password reset, APIs and legacy endpoints.
Check that sessions are invalidated on logout and after a password change.
Review token handling: signature validation, algorithm restrictions, expiry and secret strength for JWTs.
Test rate limiting against credential stuffing, and look for account enumeration in login and reset responses.
4. Test input handling
Test each input in its context: SQL and NoSQL injection, OS command and template injection, stored, reflected and DOM-based cross-site scripting, server-side request forgery (especially dangerous in cloud environments, where it can reach instance metadata services), file uploads, and unsafe deserialization.
5. Test business logic
No tool understands what your application is supposed to do. Testers look for negative quantities, skipped workflow steps, prices or discounts modified in client-side requests, and race conditions that let a coupon or balance be used twice. These flaws are invisible to scanners and often have direct financial impact.
6. Review configuration and dependencies
Check security headers, CORS policies, cookie flags and error handling. Mishandling of Exceptional Conditions is now its own OWASP Top 10:2025 category, and verbose errors frequently leak information that helps an attacker. Review third-party components and how they are sourced, built and updated, in line with the Software Supply Chain Failures category.
Validate before you report
Every finding should come with reproducible evidence, a realistic description of impact in the context of your business, and remediation guidance at the code or configuration level. A shorter report with validated findings is worth far more than a long list of unconfirmed scanner alerts.
Build it into the development lifecycle
Penetration testing works best as one layer among several: static analysis, dependency scanning and dynamic scanning in the CI pipeline, threat modeling for new features, and manual testing before major releases and at regular intervals.
Want an experienced team to test your web application? Contact us and we will help you define a realistic scope.
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