Bug bounty hunters, penetration testers and ethical hackers can earn significantly larger payouts by finding ways around file upload restrictions on modern web applications.
File upload vulnerabilities allow malicious parties to execute arbitrary code, deface websites and gain internal access to systems.
Basic techniques, such as uploading .php files, are well known, but modern apps have multiple security layers to prevent these exploits.
This article describes multiple ways in which pros can get around these defenses, including bypassing multiple validation layers, manipulating Content-Type headers, using double extensions and finding ways to exploit case sensitivity.