a-intro

SSRF occurs when a web app fetches resources from a remote location based on the user input such as URL.

If the web app relies on a user-supplied URL scheme or protocol, an attacker can perform more influencing attack.

• http:// and https://: Fetches content use HTTP/s. Attacker might use this to bypass WAFs, access restricted endpoints, or access endpoints in the internal network.
• file://: Reads a file from the local file system. Attacker might use this to read local files (LFI).
• gopher://:Sends arbitrary bytes to the specified address. Attacker might use this to send HTTP POST requests with arbitrary payloads or communicate with other services such as SMTP server or database.