Server-side request forgery

In computer security, server-side request forgery (SSRF) is a type of exploit where an attacker abuses the functionality of a server causing it to access or manipulate information in the realm of that server that would otherwise not be directly accessible to the attacker.

Similar to cross-site request forgery which utilises a web client, for example, a web browser, within the domain as a proxy for attacks; an SSRF attack utilizes an insecure server within the domain as a proxy.

Types of SSRF -

i. Basic SSRF: Here the response is displayed to the attacker.

ii. Blind SSRF: Here the response is not displayed to the attacker. (Difficult to detect at first sight)

Basic SSRF:

In this type of attack the response is displayed to the attacker. The server fetches the URL requested by the attacker and sends the response back to the attacker.

If a parameter of a url is vulnerable to this attack. It is possible the attacker can device ways to interact with the server directly (ie: via 127.0.0.1 or localhost) or with the backend servers that are not accessible by the external users.

Blind SSRF:

In this type of attack the response is not sent back to the attacker. Therefore, the attacker has to device ways to confirm this vulnerability.