Notes

Overview of HTTP:
HTTP (Hypertext Transfer Protocol) is the foundation of any data exchange on the Web and is a protocol used for transmitting hypertext requests and information on the internet. HTTP is not secure, so information is transmitted in plaintext, making it vulnerable to eavesdropping.

How Does the Internet Work?
User Enters URL:
The process begins when a user enters a URL (Uniform Resource Locator) into a web browser.
Domain Name System (DNS) Lookup:
The browser performs a DNS lookup to translate the human-readable domain name (e.g., www.example.com) into an IP address.
TCP Connection:
The browser establishes a TCP connection with the server at the IP address. This connection is used to send an HTTP request to the server.
Sending HTTP Request:
The browser sends an HTTP request to the server, asking for the desired web page or resource.
Server Processes Request:
The server processes the HTTP request and generates an HTTP response.
Receiving HTTP Response:
The browser receives the HTTP response from the server, which includes the content of the web page (HTML, CSS, images, etc.).
Rendering the Web Page:
The browser renders the web page for the user to view.
Stages of HTTP Communication:
DNS Resolution:
Translate the domain name to an IP address.
TCP Handshake:
Establish a TCP connection between the client and the server.
HTTP Request:
The client sends an HTTP request to the server.
HTTP Response:
The server processes the request and sends back an HTTP response.
What Needs to Happen Before the Browser Can Initiate the First HTTP Request?
User Inputs URL:
User enters the URL in the browser.
DNS Lookup:
The browser performs a DNS lookup to convert the URL to an IP address.
TCP Connection Establishment:
A TCP connection is established with the server at the obtained IP address.
HTTP Response Codes and Their Importance in Penetration Testing:
1xx (Informational):
Indicate that the request was received and understood and is being processed.
2xx (Success):
Indicate that the request was successfully received, understood, and accepted.
Example: 200 OK
3xx (Redirection):
Indicate that further action must be taken to complete the request.
Example: 301 Moved Permanently
4xx (Client Error):
Indicate that the request contains bad syntax or cannot be fulfilled.
Example: 404 Not Found
5xx (Server Error):
Indicate that the server failed to fulfill an apparently valid request.
Example: 500 Internal Server Error
Importance in Penetration Testing:
Understanding Server Behavior:
Response codes help in understanding the behavior and state of the server.
Identifying Vulnerabilities:
Certain response codes may indicate potential vulnerabilities (e.g., 200 OK for a page that should be unauthorized, indicating a potential access control issue).
Error Handling:
Observing how a server handles different types of requests and errors can reveal security misconfigurations or vulnerabilities.
Redirects and Flow:
Understanding the flow and redirects helps in mapping the application and identifying potential security issues.