Top 10 Web‑App Flaws You Can Find Tonight (and How to Fix Them)
Bug‑Bounty Gold, or Data‑Breach Time‑Bombs
Web applications rarely implode because of Hollywood‑style zero‑days. More often it’s tiny, obvious gaps that linger for months. Grab a laptop, install a couple of free tools, and you can spot, and patch, most of the classics in a single evening. Below are the ten vulnerabilities that show up in pentest reports (and news headlines) year after year, plus quick‑start detection and remediation tips.
Legal note: Only test apps you own or those explicitly covered by a public bug‑bounty policy.
1. Reflected Cross‑Site Scripting (XSS)
Find it: Paste <script>alert(1)</script> into search boxes and URL parameters while running Burp Suite Community’s live scanner.
Fix it: Escape output with a templating engine (e.g., React’s auto‑escaping) or add a Content‑Security‑Policy header that blocks inline scripts.
2. SQL Injection
Find it: Add ' OR 1=1-- to form fields; look for SQL errors or table dumps in responses.
Fix it: Use parameterised queries (prepared statements) and ORM frameworks; restrict DB accounts to least privilege.
3. Broken Authentication & Session Management
Find it: Intercept login requests, replay old session cookies, or guess predictable tokens.
Fix it: Rotate session IDs after login, set HttpOnly and Secure flags, enforce MFA, throttle brute‑force attempts.
4. Security Misconfiguration
Find it: Visit /phpinfo.php, /server-status, or browse exposed .git directories; run Nikto for default files.
Fix it: Remove sample apps, disable directory indexing, block admin panels from the internet, automate CIS hardening scripts.
5. Sensitive Data Exposure
Find it: Submit form data over HTTP (not HTTPS) and sniff traffic with Wireshark; hunt for plain‑text secrets in JavaScript bundles.
Fix it: Enforce HTTPS with HSTS, encrypt data at rest, move secrets to environment variables or managed vaults.
6. Broken Access Control (IDOR)
Find it: Change numeric IDs in URLs (/invoice/1001 → /invoice/1002) and watch for someone else’s data.
Fix it: Implement server‑side authorization checks on every request; use UUIDs instead of incremental IDs.
7. Unrestricted File Upload
Find it: Upload .php or .jsp shells via profile‑picture forms; attempt double‑extension tricks (shell.php.jpg).
Fix it: Whitelist MIME types, store uploads outside the web root, and scan files with antivirus before processing.
8. Server‑Side Request Forgery (SSRF)
Find it: Supply internal URLs (http://169.254.169.254/latest/meta-data) in image‑fetch or webhook fields.
Fix it: Validate destination hosts against an allow‑list, block meta‑data IP ranges, and require outgoing proxies with egress rules.
9. Cross‑Site Request Forgery (CSRF)
Find it: Observe state‑changing POST requests lacking anti‑CSRF tokens; craft an HTML form that replays them.
Fix it: Add synchroniser tokens, SameSite cookie attributes, and confirm sensitive actions with re‑authentication.
10. Using Components with Known Vulnerabilities
Find it: Run npm audit, pip-audit, or OWASP Dependency‑Check to flag outdated libraries.
Fix it: Patch or replace vulnerable dependencies; enable automated dependency‑update pipelines and staging tests.
Quick‑Start Toolkit (Free)
| Purpose | Tool | Install Hint |
|---|---|---|
| Intercept & modify traffic | Burp Suite Community | snap install burpsuite |
| Crawl & brute‑force directories | ffuf | go install github.com/ffuf/ffuf@latest |
| Detect outdated packages | OWASP Dependency‑Check | Docker image: jeremylong/owasp-dependency-check |
| Automated recon | Amass | apt install amass |
| Vulnerability scanning | Nuclei | Pre‑built release binaries |
Spin up an intentionally vulnerable VM like OWASP Juice Shop or DVWA and practise each flaw in a safe sandbox before poking at production.
For Developers: “Shift Left” Cheat‑Sheet
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Add linters that flag unsafe functions (
eval, string‑concat SQL) at commit time. -
Run DAST/SAST in your CI pipeline; break the build on critical findings.
-
Schedule quarterly dependency reviews—no one remembers library updates during feature crunches.
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Hold bug‑bash days where engineers play attacker; celebrate every flaw squashed.
Keep Learning, Keep Earning (or Securing)
The Hack Academy’s Internet Vulnerabilities course deep‑dives each weakness with lab‑based exploits, code‑level fixes, and capture‑the‑flag challenges. Whether you’re chasing your first bug‑bounty payout or locking down a SaaS platform, mastering these ten flaws turns late‑night curiosity into professional muscle.
Patch a bug tonight, prevent a breach tomorrow.
Alternatively find all our training courses HERE.