Introduction to File Upload Attacks

Types of File Upload Attacks

The most common reason behind file upload vulnerabilities is weak file validation and verification

The worst possible kind of file upload vulnerability is an unauthenticated arbitrary file upload vulnerability. With this type of vulnerability, a web application allows any unauthenticated user to upload any file type, making it one step away from allowing any user to execute code on the back-end server.

In some cases, we may not have arbitrary file uploads and may only be able to upload a specific file type. Even in these cases, there are various attacks we may be able to perform to exploit the file upload functionality if certain security protections were missing from the web application.

Examples of these attacks include:

• Introducing other vulnerabilities like XSS or XXE.
• Causing a Denial of Service (DoS) on the back-end server.
• Overwriting critical system files and configurations.
• And many others.