Server-side request forgery (SSRF) is a web security vulnerability that allows an attacker to induce the server-side application to make requests to an unintended location. This can be used to access internal resources that are not intended to be exposed to the public, such as databases, file systems, or other web applications.
SSRF attacks typically exploit vulnerabilities in the way that a web application handles user-supplied input. For example, an application might allow users to specify the URL of an external resource that the application will fetch. If the application does not properly validate the user-supplied URL, an attacker could specify a URL that points to an internal resource, such as the application's own database.
Once the attacker has tricked the application into making a request to an unintended location, they can then use the application to access sensitive data or perform unauthorized actions. For example, an attacker could use SSRF to steal database credentials, download confidential files, or even take control of the application's server.
SSRF is a serious security vulnerability that can have a significant impact on an organization. To protect against SSRF attacks, it is important to carefully validate all user-supplied input and to restrict the types of requests that an application can make.
Here are some of the most common ways that SSRF attacks are carried out:
URL parameter poisoning: This is the most common way that SSRF attacks are carried out. The attacker simply modifies the URL that is passed to the application to point to an unintended location.
Parameter tampering: This involves modifying the parameters that are passed to the application in a way that forces the application to make a request to an unintended location.
File upload: This involves uploading a file that contains a malicious URL. When the file is uploaded, the application will attempt to fetch the URL, which can be used to access an unintended location.
There are a number of things that can be done to prevent SSRF attacks, including:
Validating all user-supplied input: This is the most important step in preventing SSRF attacks. All user-supplied input should be carefully validated to ensure that it does not contain malicious code.
Restricting the types of requests that an application can make: This can be done by using a firewall or web application firewall (WAF) to block requests to certain types of URLs.
Using a proxy: A proxy can be used to intercept all requests that are made by an application. This can help to prevent SSRF attacks by ensuring that all requests are made to legitimate locations.