← All Status Codes
501
Not Implemented
🔴 Server Error
Medium Risk
📖 What Is HTTP 501?
The server does not support the functionality required to fulfill the request. The server does not recognize the request method.
🛡️ Security Implications
Ensure the server returns 501 for unsupported HTTP methods rather than attempting to process them.
🔍 Common Causes
Server does not support the HTTP method used (e.g., PATCH on an old server), or a required feature is not installed.
🔧 How to Fix
Use a supported HTTP method. Update the server software. Check if the required module/extension is installed.
🖥️ How to Check
curl -I -o /dev/null -w "%{http_code}" https://example.com