Server-side request forgery (SSRF) in Web App Penetration Testing | 2023

Understanding the Concept of SSRF in Web Application Penetration Testing for Bug Bounty | Karthikeyan Nagaraj

What is SSRF?

Server-side request forgery is a web security vulnerability that allows an attacker to cause the server-side application to make requests to an unintended location.

In a typical SSRF attack, the attacker might cause the server to make a connection to internal-only services within the organization’s infrastructure. In other cases, they may be able to force the server to connect to arbitrary external systems. This could leak sensitive data, such as authorization credentials.

What is the impact of SSRF attacks?

A successful SSRF attack can often result in unauthorized actions or access to data within the organization. This can be in the vulnerable application, or on other back-end systems that the application can communicate with. In some situations, the SSRF vulnerability might allow an attacker to perform arbitrary command execution.

An SSRF exploit that causes connections to external third-party systems might result in malicious onward attacks. these can appear to originate from the organization hosting the vulnerable application.

Common SSRF attacks

SSRF attacks often exploit trust relationships to escalate an attack from the vulnerable application and perform unauthorized actions. These trust relationships might exist in relation to the server, or in relation to other back-end systems within the same organization.

SSRF attacks against the server

In an SSRF attack against the server, the attacker causes the application to make an HTTP request back to the server that is hosting the application, via its loopback network interface. This typically involves supplying a URL with a hostname like 127.0.0.1 (a reserved IP address that points to the loopback adapter) or localhost (a commonly used name for the same adapter).

For example, imagine a shopping application that lets the user view whether an…