Security Oversights in Custom Web Apps (And How Hackers Find Them)

1. Assuming 'Private' Means Secure

One of the biggest misconceptions is that internal or low-traffic apps are safe simply because they're obscure. The reality is that attackers use automated scanners to find and map exposed endpoints across the internet - they don't target companies by name.

A forgotten staging domain, an open API route, or even a misconfigured firewall rule can expose your system to public discovery. Once that happens, hackers start probing for weak points automatically.

How to fix it:

• Keep an inventory of all subdomains, staging environments, and endpoints.
• Use access controls and network restrictions on anything not meant to be public.
• Run your own external scans periodically to see what's visible to the world.

2. Weak Authentication and Token Handling

Many custom apps roll their own authentication or session logic. It feels simple - a login form, a session cookie, maybe a JWT. But one missing setting (like HttpOnly or SameSite) or a flawed token expiration rule is enough for session hijacking.

Hackers often test these vulnerabilities using automated scripts that try common misconfigurations, expired tokens, and credential stuffing attacks.

How to fix it:

• Use well-tested authentication frameworks, not custom code.
• Enforce MFA where possible.
• Rotate and expire tokens securely, especially for API access.
• Set strict cookie attributes and use HTTPS everywhere.

3. Forgotten Admin Panels and Debug Routes

Developers often leave behind hidden routes during development: /admin, /debug, /test-api, /graphql. These endpoints sometimes have weak or no authentication - because they were meant for internal use.

How to fix it:

• Audit routes before every deployment.
• Disable debug or test endpoints completely in production.
• Restrict admin panels behind VPNs or IP whitelists.

4. Missing Input Validation and Sanitization

This is the oldest security issue in the book, and it's still the most common. Developers trust user input too easily, assuming that if the UI is clean, the data must be too. Attackers bypass front-end controls and send malicious payloads directly to the backend.

From classic SQL injection to newer template and JSON injection attacks, the entry points are endless.

How to fix it:

• Sanitize and validate every piece of input, including API requests.
• Use ORM libraries that handle query parameters safely.
• Adopt a security-first mindset: never trust user data.

5. Poor API Security

Most web apps today expose APIs, either for frontend communication or external integrations. APIs are often built quickly - and tested minimally.

Common API oversights include missing authentication, unclear rate limits, unencrypted data, or verbose error messages that leak sensitive details. Attackers use API fuzzing tools to send thousands of malformed requests, mapping how your app responds and looking for inconsistencies.

How to fix it:

• Use API gateways and authentication middleware.
• Limit payload sizes and request rates.
• Avoid sending stack traces or internal error details to the client.

6. Incomplete Logging and Monitoring

Security failures often go unnoticed because no one's watching. Many custom apps log errors but not suspicious behavior - failed logins, privilege escalations, or unusual request patterns. By the time a breach is discovered, it's weeks or months too late.

How to fix it:

• Centralize logging using tools like ELK or Datadog.
• Monitor for repeated failed logins or privilege misuse.
• Set alerts for unusual IP activity or high API call volume.

7. Outdated Dependencies

Every modern app relies on open-source libraries. The problem is that once they're installed, they're often forgotten. A single outdated package with a known CVE (Common Vulnerabilities and Exposures) can make your entire system exploitable.

How to fix it:

• Automate dependency checks using tools like Dependabot or Snyk.
• Keep a schedule for updates and vulnerability scanning.
• Avoid using unmaintained packages altogether.

8. No Formal Security Testing

Most internal teams rely on functional testing - does the feature work? But security testing asks a different question: what happens when someone tries to break it?

Without penetration testing, SAST (Static Application Security Testing), or DAST (Dynamic Application Security Testing), you're essentially hoping vulnerabilities don't exist rather than confirming they don't.

How to fix it:

• Run automated security scans as part of your CI/CD pipeline.
• Schedule penetration tests before major releases.
• Implement code review processes that include security checks.
• Train developers on OWASP Top 10 and secure coding practices.

Building Secure by Default

Security doesn't have to feel like a checklist you tackle after everything else is done. The most secure applications are built with security principles embedded from the start - not as an afterthought.

Core principles for secure development:

• Least privilege: Give users and services only the access they absolutely need.
• Defense in depth: Layer multiple security controls so one failure doesn't compromise the whole system.
• Fail securely: When something goes wrong, default to denying access rather than granting it.
• Audit everything: Log security-relevant events so you can detect and respond to incidents.
• Stay updated: Security is not a one-time setup - it requires continuous vigilance.

The challenge for most internal teams is that security expertise isn't something you can hire easily or learn overnight. It requires experience across infrastructure, application logic, compliance frameworks, and threat modeling.