4.3 Query String Filtering

📖 Overview

The Query String Filtering module enables you to control and sanitize the query parameters (GET variables) attached to incoming requests.

By defining allowed or blocked query strings on a per-path basis, you can protect sensitive endpoints, APIs, and web forms against tampering, injection, or unexpected behavior.

This adds a powerful application-layer control that complements WAF rules and general request validations.

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🎯 Purpose

• Allow only expected parameters on specific pages.

• Block unexpected or malicious parameters.

• Remove untrusted query parameters automatically.

• Harden API endpoints, authentication flows, and payment pages.

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✅ How It Works

You define rules specifying:

• Target Page Path: (e.g., /login, /api/user/info, /checkout)

• Allowed Query Keys: (e.g., email, token, id)

When a request is made:

• Only the listed keys are allowed.

• Any additional parameters are either removed or blocked based on configuration.

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📋 Example

Allowed Keys for /login

• email

• redirect_uri

Incoming Request:

/[email protected]&admin=true

Behavior:

• admin=true is removed or causes a block, depending on rule setting.

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🛠️ Configuration Options

• Allow Only These Keys: Block or strip any parameter not explicitly listed.

• Action Mode:

  • Remove unauthorized arguments silently

  • Block the request if unauthorized arguments are detected

• Multiple Rules: Create multiple rules for different paths.

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🚀 Use Cases

Scenario	Benefit
Protect login and signup endpoints	Prevent parameter injection
Secure API requests	Enforce strict parameter structure
Harden payment callbacks	Only allow signed, expected arguments
Reduce attack surface	Disallow noisy or unnecessary parameters

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🧠 Best Practices

• Whitelist only absolutely necessary parameters.

• Avoid allowing “debug”, “test”, or unused parameters on production systems.

• Combine Query String Filtering with WAF to maximize protection.

• Review URL patterns regularly as your application evolves.

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⚙️ How to Add a Query String Filter

1. Go to Security Rules > Query String Filtering.

2. Click Add New Rule.

3. Enter the Page Path.

4. Define all allowed query keys.

5. Choose the action (Remove unauthorized / Block unauthorized).

6. Save the rule.

🛡️ The rule will be active immediately for all matching requests.

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⚡ Important Notes

• Query filtering happens before request routing to backend servers.

• Filtering is case-sensitive for parameter names.

• Be cautious on dynamic URLs where parameters may vary unexpectedly.

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🎯 By enforcing strict query string structures, you prevent misuse, abuse, and accidental exposure of your application's internal logic.