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5 Advanced Ways I Test for File Upload Vulnerabilities
File upload vulnerabilities remain one of the most dangerous entry points for attackers, as poorly implemented upload mechanisms can lead to remote code execution, privilege escalation, or server compromise. Testing for these vulnerabilities requires an understanding of both the application logic and underlying server configurations.
In this blog, I’ll cover 5 advanced ways to test for file upload vulnerabilities, with explanations, methods, and code snippets. These techniques are useful for both penetration testers and security researchers.
1. Testing for File Extension Manipulation
File extension checks are often the first line of defense in many file upload mechanisms. Developers typically allow uploads of certain file types such as .jpg, .png, or .pdf, assuming that restricting file types ensures security. However, this approach can be bypassed if the server checks the file extension but doesn't properly validate the file's content.
How It Works:
Attackers can upload a malicious script by changing its file extension to something benign. For example, renaming malicious.php to malicious.jpg could fool a server that only checks extensions and not the actual content.
