How to Protect Your Web App from Malware via File Uploads

If your web application has an <input type="file"> tag anywhere in its architecture, you have a massive target on your back. File upload features are essential for modern applications—whether it’s uploading a profile picture, a CSV of user data, or a PDF report. However, if improperly handled, a simple file upload form is the easiest way for an attacker to achieve Remote Code Execution (RCE), deface your server, or distribute malware to your users. In this post, we are going to look at the real-world vulnerabilities associated with file uploads and build a "defense in depth" strategy to secure them. The Threat Landscape: What Can Go Wrong? When you allow a user to upload a file, you are inherently allowing them to write data to your disk. If you blindly trust the file they provide, you open yourself up to: Web Shells (RCE): An attacker uploads a .php or .jsp file containing a malicious script. If your server executes it, they own your machine. Directory Traversal: An attacker intercept