Do not trust the Content-Type header, as it can be spoofed; instead, inspect the actual file contents to verify its type.
Only allow a strictly defined list of safe file extensions.
Large files can be used to perform Denial of Service (DoS) attacks by exhausting server storage or memory. "Hot" Strategies for Securing File Uploads fileupload gunner project hot
Automatically rename files upon upload to prevent predictable paths and avoid execution of malicious filenames.
To mitigate these risks, the project and industry leaders like the OWASP Foundation recommend several "hot" mitigation strategies: Do not trust the Content-Type header, as it
Attackers can upload malicious scripts (like web shells) that execute on the server, potentially leading to a complete system takeover.
At its heart, the Fileupload Gunner project addresses the risks when a web server allows users to upload files to its filesystem without sufficient validation of their name, type, or contents. The consequences of these vulnerabilities can be severe: The consequences of these vulnerabilities can be severe:
Set strict maximums for both filename length and overall file size.
Uploaded files may contain code designed to infect the system or other users.