How to block specific User-Agent in ASM Policy

To block a user agent containing "curl", you can typically implement a rule in your web server configuration that identifies any user agent string with the word "curl" and denies access to your website from that source; depending on your server setup, this might involve creating a firewall rule or using a web application firewall (WAF) to filter based on the "User-Agent" header containing "curl". 

Key points to remember:
Identifying the "curl" pattern:
Look for the exact string "curl" within the User-Agent header, as it's usually the most reliable indicator of a curl request. 

Implementation methods:
Web server configuration: Most web servers like Apache, Nginx, and Microsoft IIS allow you to set custom rules based on the User-Agent header to block specific patterns. 

WAF (Web Application Firewall): If your website uses a WAF like Cloudflare, you can create a blocking rule specifically targeting User-Agents containing "curl". 
Example rule (Nginx):
Code

location / {

    if ($http_user_agent ~* "curl") {

        return 403;

    }

    # Your regular website content serving code here

}

Important considerations:
False positives:
Be careful not to accidentally block legitimate users who might have a browser that happens to include "curl" in its User-Agent string (although this is uncommon). 
Alternative methods:
IP blocking: If you suspect a specific IP address is using curl for malicious activity, you can block that IP directly instead of relying solely on the User-Agent. 
Rate limiting: Implement rate limiting to prevent excessive requests from any single source, including curl-based bots.

HTH
F5 Design Engineer

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